Glass 

Book 'Vy5C 

PRESENTED BY 



i 



DEVELOPMENT AND ACTIVITIES OF ROOTS OF 

CROP PLANTS 



A STUDY IN CROP ECOLOGY 



BY 

John E. Weaver, Frank C. Jean, and John W. Crist 




Published by the Cahnegie Institution of Washington 
Washington, May, 1922 

Monograph 



DEVELOPMENT AND ACTIVITIES OF ROOTS OF 

CROP PLANTS 

my £ 

A STUDY IN CROP ECOLOGY 



BY 

John E. Weaver, Frank C. Jean, and John W. Crist 




Published by the Carnegie Institution of Washington 
Washington, May, 1922 




CARNEGIE INSTITUTION OF WASHINGTON 
Publication No. 316 



Copies of this book 

first issued 
MAY 1 1 1922 



isatitatSant 
HAY t2 1922 



TECHNICAL PRESS 
WASHINGTON, D. C. 



5 

CONTENTS. 

Page 



List of illustrations v 

Introduction 3 

I. Investigations at Peru, Nebraska, in 1919. 

University No. 21 oats, Avena sativa 8 

Swedish Select oats, Avena sativa 11 

Durum wheat, Triticum durum 13 

Marquis wheat, Triticum cestivum 15 

Manchuria barley, Hordeum vulgar e 18 

Corn, Zea mays indentata 21 

Earlier investigations of corn 25 

Potato, Solanum tuberosum 26 

Earlier investigations of potatoes 29 

Comparison of root systems 30 

Environmental conditions of growth 32 

Summary of root development 38 

II. Investigations at Lincoln, Nebraska, in 1919 and 1920. 

Oats, Avena sativa 41 

Barley, Hordeum vulgare , 48 

Wheat, Triticum cestivum 49 

Alfalfa, Medicago sativa 52 

Sweet clover, Melilotus alba 54 

Comparison of root systems 55 

III. Investigations at Phillipsburg, Kansas, in 1920. 

Oats, Avena sativa 57 

Barley, Hordeum vulgare . . . . | 59 

Wheat, Triticum cestivum . . . . 59 

Alfalfa, Medicago sativa 60 

Sweet clover, Melilotus alba. . 60 

Summary of crop development 60 

IV. Investigations at Burlington, Colorado, in 1920. 

Wheat, Triticum cestivum 62 

Oats, Avena sativa 67 

Barley, Hordeum vulgare 68 

Alfalfa, Medicago sativa 69 

Sweet clover, Melilotus alba 70 

Summary of crop development 71 

Summary of environment and crop development at all stations, 1920 72 

V. Investigations at All Stations in 1921. 

Investigations at Peru, Nebraska 78 

Investigations at Lincoln, Phillipsburg, and Burlington 80 

Summary of environment and crop development 87 

Correlation of crop development with that of native vegetation 89 

VI. Depths at which Plants absorb Water and Nutrients. 

Preliminary experiments 93 

Field experiments, 1920 94 

Greenhouse experiments, 1920-21 100 

Field experiments, 1921 105 

Summary 114 

Bibliography 110 

in 



LIST OF ILLUSTRATIONS. 



PLATES. 

Plate 1. 

A. Iowa Silver Mine corn 57 days old; root system shown in fig. 8. 

B. Potato 2.3 feet high on July 8; root system shown in fig. 11. 

C. Corn on September 2; root system shown in fig. 9. 

D. Trench used in examining the roots of cereals. 
Plate 2. 

A. Marquis Spring wheat at Burlington, 1920. 

B. Marquis Spring wheat from a square meter at Burlington (left), Phillipsburg, and 

Lincoln. 

Plate 3. 

A. White Kherson oats from a square meter at Burlington (left), Phillipsburg, and 

Lincoln. 

B. Manchuria barley from a square meter at Burlington (left), Phillipsburg, and 

Lincoln. 

Plate 4. 

A. Four hundred plants of alfalfa from lower crop plats (left) and upper crop plats 

at Lincoln; and from Phillipsburg and Burlington, respectively. 

B. Three hundred plants of sweet clover from lower crop plats (left) and upper crop 

plats at Lincoln; and from Phillipsburg and Burlington, respectively. 

Plate 5 

A. Wheat from Lincoln (left), Phillipsburg, and Burlington, May 18-21. 

B. Barley from Lincoln (left), Phillipsburg, and Burlington, May 18-21. 
Plate 6. 

A. Oats at Lincoln, May 18. 

B. Oats at Phillipsburg, May 19. 

C. Oats at Burlington, May 20. 
Plate 7. 

A. Wheat from Lincoln (left), Phillipsburg, and Burlmgton, June 10. 

B. Barley from Lincoln (left), Phillipsburg, and Burlington, June 10. 
Plate 8. 

A. Oats at Lincoln, June 10. 

B. Oats at Phillipsburg, June 10. 

C. Oats at Burlington, June 10. 
Plate 9. 

A. Barley grown in container with wax seals at 6-inch intervals. 

B. Same with upper portion of container removed. 

C. Wax seal at depth of 2 feet (left) showing the penetration of the seal by roots and 

their abundance under field conditions. Fertilized soil at 2.5 feet depth 
filled with copiously branched roots. 

D. Arrangement of containers in greenhouse experiment, 1920-21. 
Plate 10. 1 r ... _ 

A. Development of barley on December 11 m unaerated, fertilized soil. 

B. Development of barley on December 11 in aerated, unfertilized soil. 
Plate 11. 

A. Development of crop on March 12 in fertilized soil. 

B. In unfertilized soil. 
Plate 12. 

A. General view of one row of containers, May 17. 

B. Detailed view of barley and potatoes, May 17. 
Plate 13. 

A. Potatoes and barley on June 13. 

B. Native grasses on August 15, at the time of examination. 
Plate 14. 

A. Development of corn, June 5. 

B. Development of corn, July 10. 



List of Illustrations. 



v 



TEXT-FIGURES 

Page 

1. (A) Root system of University No. 21 oats 59 days old; (B) Swedish Select 

oats 60 days old 10 

2. (A) University No. 21 oats; (B) Swedish Select oats; at maturity 12 

3. (A) Marquis wheat 20 days old; (B) 70 days old; (C) Durum wheat 60 days old . 14 

4. (A) Durum wheat; (B) Marquis wheat; at maturity 16 

5. (A) Manchuria barley 20 days old; (B) 54 days old 19 

6. Manchuria barley at maturity 20 

7. Root system of Iowa Silver Mine corn 36 days old 21 

8. Root system of corn on July 5 • • 23 

9. Root system of corn on September 2 facing 24 

10. One-half of root system of a potato plant 56 days old 27 

11. One-half of root system of a mature potato plant 28 

12. Water-content in excess of hygroscopic coefficient from March 31 to June 16 34 

13. Water-content in excess of hygroscopic coefficient in the several crop plats 

on May 30 34 

14. Water-content in excess of hygroscopic coefficient in the several crop plats 

on June 23 35 

15. Soil-temperatures at various depths during 1919 37 

16. Average day and night temperatures (solid lines) and average maximum and 

minimum temperatures 37 

17. Oats 31 days old 42 

18. Oats 45 days old 43 

19. Oats 60 days old ■ 44 

20. Average daily air temperature (long broken lines), soil temperature (short 

broken lines), and humidity (solid line), 1920 46 

21. (A) Oats; (B) wheat; at time of blossoming facing 46 

22. Wheat 31 days old 50 

23. (A) Wheat 45 days old; (B) 60 days old 51 

24. (A) Alfalfa 63 days old; (B) sweet clover 63 days old 53 

25. (A) Alfalfa 132 days old; (B) sweet clover 115 days old 55 

26. Average day and average night air temperatures and average daily soil 

temperature (broken line) at Phillipsburg, 1920 59 

27. Wheat roots showing normal differences in branching at Lincoln, L, and 

Burlington, B. 1, at depth of 1.5 feet; 2, root-ends 64 

28. Average day and average night air temperatures and average daily soil 

temperature (broken line), Burlington, 1920 65 

29. Average day humidity (lower lines) and average night humidity (upper lines) 

at Lincoln (solid lines), and Burlington (broken lines), 1920 66 

30. Oats at maturity, Burlington, 1921 67 

31. Alfalfa excavated at Burlington, June 28, 1921, during the second year of 

growth 69 

32. Mean precipitation in inches (black) and precipitation for 1920 at Lincoln 

(left), Phillipsburg, and Burlington 72 

33. Average daily soil temperature at Lincoln (solid line), Phillipsburg (long 

broken lines), and Burlington (short broken lines), 1920 73 

34. Average daily air temperature at Lincoln (solid line), Phillipsburg (long 

broken lines), and Burlington (short broken lines), 1920 73 

35. Hygrothermograph records from Lincoln (upper) and Burlington, June 1921; 

light lines temperature, heavy lines humidity 74 

36. Average daily evaporation at Lincoln (solid line), Phillipsburg (long broken 

lines), and Burlington (short broken lines), 1920 75 

37. Average day air temperatures (heavy lines) and average night temperatures 

(light lines) at Lincoln (solid lines), Phillipsburg (long broken lines), 

and Burlington (short broken lines), 1921 83 



VI 



List of Illustrations. 



TEXT-FIGURES — continued . 

Page 



38. Average daily evaporation at Lincoln (solid line), Phillipsburg (long broken 

lines), and Burlington (short broken lines), 1921 84 

39. Mean precipitation in inches (black) and precipitation for 1921 at Lincoln 

(left), Phillipsburg, and Burlington 87 

40. Diagram of containers and development of barley, 1920. Positions of wax 

seals, 6 inches apart, indicated by the cross-lines 94 

41 Average daily temperature (long broken lines), humidity (upper solid line), 

and average daily evaporation at Lincoln, 1921 106 

42. Diagram of containers and root development of crops, 1921. Horizontal 

lines (6 inches apart, except in last two) indicate position of wax 

seals and double vertical lines position of nutrients 107 



DEVELOPMENT AND ACTIVITIES OF ROOTS OF 

CROP PLANTS. 

A STUDY IN CROP ECOLOGY. 



BY 

John E. Weaver, 

Professor of Plant Ecology in the University of Nebraska, 

Frank C. Jean, 
Professor of Botany in the Peru (Nebraska) State Normal School, 

and 

John W. Crist, 
Instructor in Botany in the University of Nebraska. 



1 



DEVELOPMENT AND ACTIVITIES OF ROOTS OF 
CROP PLANTS. 



INTRODUCTION. 

Some of the most fundamental problems of plant ecology in its mani- 
fold relations to crop production are those concerned with root development 
and the relations of roots to soil and subsoil. An exact knowledge of the 
root development of crop plants, of their position, extent, and activity as 
absorbers of water and solutes at various stages of growth, is of paramount 
inportance to a scientific understanding of plant production. Moreover, a 
knowledge of modifications produced by variations in the subterranean 
environment, whether due to such natural conditions as excessive water- 
content or drought, or to tillage or fertilizers, is of no less importance. In 
fact, many processes and practices will cease to be empirical and come to 
be exact only when the relation of roots to soil is recognized as having funda- 
mental value. 

The importance of root extent and distribution in a study of soil-moisture 
is patent. These should determine not only what depth of sample should 
be used, but also the maximum depth to which samples should be obtained. 
The time, method, and amount of the application of water for irrigation 
studied in the light of root development furnish a rich and varied field for 
investigating problems of the greatest scientific and economic importance. 
Conversely, the proper drainage of swamps and boglands for pastures, 
meadows, afforestation, or for cultivated crops, should be determined with 
reference to root relations. (Cf. Howard, 1916, 1918; Osvald, 1919.) 

A knowledge of root systems is again fundamental in the scientific applica- 
tion of fertilizers. In fact, it should furnish the criterion not only for time 
and amount, but also in regard to the manner and depth of such application. 
In securing soil samples for chemical analysis, root extent and activity at 
different levels should determine the depth at which the samples are taken. 
Moreover, it will clear up the whole problem of the relative values that should 
be placed upon chemical analysis of surface soil and subsoil. 

Preliminary studies of root systems of native plants in soils impregnated 
with alkali point out clearly that the adaptation of plant to habitat is often 
largely one of root distribution above or below the layers of greatest salt 
concentration. With adequate knowledge of the variability of the root 
systems of different varieties of crop plants, selection of those most suitable 
for cultivation in such areas should be less difficult. 

In problems of crop production on acid soils, if attacked from the more 
modern and logical viewpoint of lime requirement of the plant, rather than 
that of the soil, the root system again plays a decisive role. The lime require- 
ment of the plant is determined not only by its lime-content and rate of growth, 
but especially by its feeding power for lime. The latter is in proportion to 
the character and extent of the root system, the internal acidity of roots, 



3 



4 Development and Activities of Roots of Crop Plants. 



and their excretion of carbonic acid (Truog, 1918). A knowledge of root 
position and extent is of prime importance in studies of aeration and the 
closely allied phenomenon of soil toxicity. Passageways left in the soil, 
after the roots have decayed, afford greatly increased possibilities for aeration. 

The important problem of the relation of various methods of tillage to root 
development is one of which we are almost entirely ignorant. The value of 
various depths of plowing, listing, or subsoiling, and the preparation of the 
seed-bed, as well as the time, depth, and manner of subsequent cultivation, 
is judged entirely by the increase or decrease in growth and yield of the 
above-ground parts with scarcely a thought as to the more direct cause, the 
effect of these practices upon root activities and development. It should be 
clear that a knowledge of root development under each of the diverse methods 
of tillage, systems of mulching, etc., will not only give a logical answer for the 
results obtained by these practices, but will form a scientific basis for the appli- 
cation of other methods or combinations which may result in greater yields. 

Crop rotations on different types of soil and under different climatic con- 
ditions should be worked out with constant reference to root relations. It 
may be found practicable, especially in semiarid regions, to grow short-rooted 
and densely-rooted crops alternately with those of longer and more spreading 
root systems. In humid regions, under intensive agricultural conditions, 
two such crops might be grown in the same field at the same time. In fact, 
this is a common practice in India, where mixed cultures usually outyield 
pure ones. The selection, breeding, and adaptation of crops for arid and 
semiarid regions should logically center about their efficiency as absorbers 
and conservers of water. Plasticity of root systems as to depth, lateral 
spread, degree of branching, etc., goes far toward determining the ability of 
a crop to make sufficient growth and yield to warrant its cultivation in dry 
lands. Moreover, under these conditions root competition is an important 
factor in determining the rate of seeding. 

It seems not improbable that some of our best yielding crops may be able 
to outstrip others largely because of their greater efficiency in securing a larger 
and more constant supply of water and nutrients. Why certain artificial 
mixtures of grasses and other herbs may thrive in pastures and meadows, 
while others do less well, must depend to a large degree upon competition of 
root systems. This is the case in native grassland, where it is usual for 200 
to 300 individuals or groups of individual plants to grow in a single square 
meter, due to lessened competition resulting from absorption at different 
soil-levels and from maximum above-ground activities at different times of 
the growing-season. 

Just as a knowledge of root systems of native plants makes far more exact 
their value as indicators of lands with the possibility of crop production, 
likewise this knowledge of underground parts is of great value in solving 
problems of soil erosion, whether by wind or by water. This holding of the 
soil for cultivation applies equally to plants of pasture and meadow lands 
and to a certain extent to annual crops. Likewise, keeping the soil free from 
noxious weeds, and especially perennials, is again a problem concerned pri- 
marily with underground plant parts. 

The relation of the disease resistance of crop plants to root development 
is an important one and warrants thorough study. Recent investigations 



Introduction. 



5 



have demonstrated a close relation between the vigor of root growth and 
disease resistance. Where the disease is physiological, resulting from mal- 
nutrition or insufficient aeration, this relation is at once apparent. It seems 
certain, in the light of recent investigations, which show the extensive nature 
of the roots of most crop plants, that the results of many experiments, where 
plants were grown in pots or even relatively large containers, may have more 
apparent than real values when the work is repeated under field conditions. 
A thorough study of root distribution and absorption under cropping condi- 
tions will throw much light upon the relative value of greenhouse experiments 
on soil fertility, where containers of various sizes with either surface soil or 
subsoil were used. Even plant-breeding or crop-production experiments 
conducted in the field in small adjacent plats or by the row per ear or head 
method, undoubtedly have been affected and the results in many cases 
vitiated by the factor of root competition. 

The importance of a thorough investigation of root development and root 
activities need not be pointed out in greater detail. In preceding volumes 
(Weaver, 1919, 1920) the relation of a knowledge of root systems to plant 
production in its broader sense has been emphasized. The underground 
parts of 1,500 native plants of forest, chaparral, sandhills, plains, and prairie 
have been studied with a view to acquiring fundamental knowledge of value 
in the solution of many problems of crop production. Outstanding among 
these are range management and improvement, involving that complex 
phenomenon termed plant succession; afforestation and reforestation; and 
indeed the whole problem of land classification based upon indicator signifi- 
cance of native vegetation. Such studies through an extended region, such 
as our grassland formation, afford an excellent background for investigations 
of crop plants grown in any part of the area. For a knowledge of root posi- 
tion of native plants, especially when interpreted in their community rela- 
tions, so clearly reflects the moisture conditions of the soil that it aids not 
only in selecting the kind of crop to be most profitably grown, but also helps 
in determining the proper methods of tillage. This is especially true when 
the root habits of crop plants are also known and the degree to which they 
are modified by the environment. An extended study of the root systems of 
cereals from the Missouri to the Rocky Mountains has been reported and 
their growth habits correlated with the environment as indicated by the 
native vegetation. Moreover, the variations of root development of many 
species of crop plants on upland and lowland have been worked out in a 
preliminary manner (Weaver, 1920). 

This book may be considered a continuation of "Root Development in the 
Grassland Formation.' ' The investigations here recorded were carried out 
during the growing-seasons of 1919 to 1921. Stations were selected at Peru 
and Lincoln, Nebraska, at Phillipsburg, Kansas, and at Burlington, Colorado. 
These stations have a mean annual precipitation of about 33, 28, 23, and 17 
inches, respectively. The differences in climate are clearly expressed in the 
type of natural vegetation. The true prairies at Lincoln give way southeast- 
ward along the Missouri near Peru to the subclimax prairie, which is poten- 
tially chaparral or woodland, the grasses having possession only because of 
such disturbances as grazing, fire, mowing, etc. At Burlington, in eastern 
Colorado, a typical expression of the short-grass plains is found, while in 



6 Development and Activities of Roots of Crop Plants, 

north-central Kansas at Phillipsburg short-grasses intermingle with the taller 
ones and constitute mixed prairie (Clements, 1920, 114; Weaver, 1920 12). 
Crops were grown at the several stations under measured environmental con- 
ditions for the purpose of determining not only the nature of the root system, 
but especially also its distribution and extent at various stages of growth. 
The work was conducted under field-crop conditions and methods of tillage 
in order that the results might faithfully portray the root relations of crops 
as grown under usual farm practice. Moreover, extensive experiments have 
been conducted both in the greenhouse and under field conditions to deter- 
mine the active working-level of the roots of cereals and other crop plants as 
regards the absorption of water and nutrients at various stages in their 

gr Th^method used in excavating root systems was the same as that employed 
during the past six years. By the side of the plants to be examined a trench 
was dug to a depth of about 5 feet and of convenient width. This affords an 
open face into which one may dig with a hand-pick and other appropriate 
apparatus and thus make a careful examination of the entire root system. 
This apparently simple process, however, requires much practice, not a little 
patience, and wide experience with soil texture. In every case several plants 
were examined, often 10 or more at any given stage of development, to insure 
an adequate idea of the general root habit. Among this number it was pos- 
sible to secure some root systems in their entirety. In cases where recon- 
struction was necessary, this was rendered more accurate and less difficult 
by methods of record in the field. As the work of excavation progressed, 
the trench was deepened, so that finally the soil underlying the deepest roots 
was undercut for several inches and carefully examined as it was removed to 
assure certainty as to the maximum depth of the root-ends. Frequently the 
trenches reached depths of 5 to 9 feet. 

The usual practice was followed of writing a working description of the 
root system after several plants had been examined and then noting any 
variation from this description as more roots were excavated. This checking 
of the description in the field leads to a high degree of accuracy, for if any 
point regarding the root habit remains indefinite, opportunity is offered for 
further study. This is absolutely essential in developmental studies. 

Drawings of the root systems were made with pencil in the field on a large 
drawing-sheet and then retraced with India ink. They were made simultane- 
ously with the excavating of the roots and always to exact measurement. In 
the drawing the root systems are arranged as nearly as possible m the 
natural position in a vertical plane; that is, each root is placed in its natural 
position with reference to the surface of the soil and a vertical line from the 
base of the plant. In the case of potatoes the roots were so abundant that 
to depict all of them led to confusion, so that in the drawings of these plants 
only one-half of the root system is shown. 

In every case it was sought to illustrate the average condition of root devel- 
opment rather than the extreme. Although the drawings were made on a 
large scale, the rootlets were often so abundant that it was quite impossible 
to show the exact number as determined by average root-counts, buch 
drawings, however, carefully executed, represent the extent, position, and 
minute branching of the root system even more accurately than a photograph, 



Introduction. 



7 



for under the most favorable conditions, especially with extensive root sys- 
tems, the photograph is always made at the expense of detail, many of the 
finer branches and root-ends being obscured. 

The writers wish to acknowledge the faithful assistance of Miss Annie 
Mogensen and Mrs. F. C. Jean in the execution of the drawings of the root 
systems. Grateful acknowledgment is made to Professor J. C. Russel, of the 
Department of Agronomy of the University of Nebraska, for many helpful 
suggestions in connection with the analyses of soils and the experiments con- 
concerning the absorption of nutrients, as well as for the generous use of his 
laboratories in pursuing this phase of the work. To Mr. O. R. Clark we are 
indebted for valuable field assistance during 1920, and to Mr. E. Y. Lipetz 
for the translation of certain papers from the Russian. It is a pleasure to 
acknowledge the helpful suggestions given by Dr. F. E. Clements and Dr. 
R. J. Pool throughout the period of the work. To both Dr. Clements and 
Professor T. J. Fitzpatrick the writers are indebted for the reading of the 
manuscript and proof. 



8 



Development and Activities of Roots of Crop Plants. 



L INVESTIGATIONS AT PERU, NEBRASKA, IN 1919. 

Studies of the root development of plants at Peru were conducted during 
the season of 1919. The crops used were as follows: two strains of oats 
(Avena sativa), White Kherson and Swedish Select; two species of wheat, 
Durum (Triticum durum), and Marquis Spring (Triticum cestivum) ; Manchu- 
ria barley (Hordeum vulgare); Early Ohio potatoes (Solanum tuberosum); and 
Iowa Silver Mine corn (Zea mays indentata). These were grown on an up- 
land area of silt-loam soil, which lay near the top of a hill on a gentle western 
slope. The field, which had formerly been a bluegrass pasture, had been 
broken three years previously and the plants grown for these investigations 
were a fourth crop. Potatoes had been grown the preceding year, and the 
soil was in excellent tilth when the crops were planted. The surface 1 to 1.5 
feet consisted of a dark-colored silt-loam. This was underlaid by a very 
mellow loess to a depth of many feet. 

The crops were planted in plats 200 feet long and 30 feet wide, each con- 
taining approximately 0.14 acre. These extended in an east-and-west direc- 
tion. Corn and potatoes occupied the plats on the south side of the field. 
The smaller cereals were planted with a grain-drill at a depth of about 4 
inches. The rate of seeding in pounds per acre was as follows: Umversity 
oats 64, Swedish Select oats 48, barley 48, Marquis spring wheat and Durum 
wheat, 60. The corn was drilled in rows 3 feet apart at a depth of 3.5 inches, 
the kernels being placed 1.4 feet apart in the row. The potatoes were also 
planted in rows 3 feet apart, the space between the sliced tubers being 2 feet. 
They were covered with 3 inches of soil. 

Preparatory to planting, the plats were plowed to a depth of 5 or 6 inches 
on March 29 or April 4, and immediately harrowed. All of the crops, except 
corn, were planted at once without further preparation of the seed-bed. The 
latter was planted on May 9, after the plat had again been harrowed. 

University No. 21 Oats, Avena sativa. 

This is a special strain of the Kherson oats developed and named by the 
Department of Agronomy at the University of Nebraska College of Agri- 
culture. It is known especially for its heavy yielding qualities. 

The first examination of this oat was made April 18, 18 days after planting. 
Each plant had a single leaf, which had been above ground about 8 days and 
had an average height of 1.5 inches. The number of roots was 3 or 4. In 
most plants there appeared to be a main root that took an almost vertically 
downward course. In position it resembled a tap-root, but in structure and 
appearance was not unlike the others. Its length varied from 4 to 6 inches 
and all its characters indicated that it was the primary root. The other roots, 
while taking a general course downward, did not follow the perpendicular 
so closely. Instead, they descended at various angles from the vertical to 
a distance of 1 to 5 inches. In some cases they ended 3 inches from the ver- 
tical and 3 to 6 inches below the surface. No branches had yet appeared. 
The roots pursued a gently curving course through the loose soil. They 
were about 1 to 1.5 mm. in diameter and were densely covered with root- 
hairs to within 5 mm. of the tips. These hairs were borne so profusely and 
clung to the soil particles so tenaciously that when the roots were excavated 
and suspended they presented the appearance of small columns of earth. 



Investigations at Peru, Nebraska. 



9 



Growth conditions during this period were rather unfavorable. Cloudy, 
wet weather prevailed. At no time was the water-content of the surface 
foot of soil less than 17 per cent above the hygroscopic coefficient. The tem- 
perature of both air and soil was low. The maximum soil temperature of the 
surface foot did not exceed 62° F. However, the period was free from frost, 
the lowest air temperature being 37° F. 

The second examination of this oat was made May 29, 59 days after plant- 
ing. The plants averaged 1 to 1.2 feet in height and the number of stalks, 
including tillers, varied from 1 to 3. The first 7 to 9 inches of soil was filled 
with a complete network of fine roots and rootlets. Most of these came 
from a node a short distance below the surface and were branched freely 
to the first and second orders. They penetrated the soil in all directions from 
the base of the plant. The branches of all degrees seemed to grow upward 
as readily as downward, and the tips of those extending upward very often 
lay just beneath the soil surface. Indeed, it was not unusual to find even 
some of the larger roots lying at a depth of only 0.5 to 1 inch. The horizontal 
roots ran outward to a distance of 6 to 12 inches, and then some turned 
downward. From each plant one or two of the main roots pursued a some- 
what irregular course into the subsoil, often reaching depths of 3 to 3.4 feet. 
The maximum penetration was 3.6 feet. These longer roots were rather 
densely branched and rebranched, although not to so great a degree as those 
nearer the surface. Branches of the first order sometimes reached a length 
of 4 inches. The last 4 to 8 inches of the main roots were unbranched. Fig- 
ure 1 a shows the two portions of this root system and also indicates how 
splendidly the plant is equipped for absorption in both the upper and lower 
layers of soil. 

The month of May was cool and dry, and during this second period of root 
development all of the small cereals grew vigorously. 42 per cent of the days 
were clear, and there were only 1.8 inches of rain. The day air temperature 
averaged 65° F., the night temperature 53° F. Records of air temperature 
were obtained, as at the other stations, by means of Friez's thermographs, 
placed in appropriate shelters of the Weather Bureau type, with the record- 
ing apparatus at a height of 4 inches above the soil surface. Livingston's 
standardized, white, cylindrical, porous-cup atmometers were employed to 
measure the evaporating power of the air. The cups were operated in dupli- 
cate in the usual manner, with the evaporating surface only 3 or 4 inches above 
the surface of the soil. Because of the cool weather, the average daily evapo- 
ration was only 21 c. c. The soil temperature to a depth of 3 feet averaged 
60° F. Although there was a deficit in rainfall of 3.6 inches below the mean, 
the soil had been so thoroughly wetted during April that samples during May 
showed an average available moisture-content of 16 per cent in the first 3 
feet. The plants had a dark-green color and produced a luxuriant growth of 
leaves. 

A final examination of oats was made July 1, 92 days after planting. The 
height of the stalks, which averaged 1 to 3 per plant, ranged from 2.8 to 3.2 
feet. The crop was about half ripe. In general, the form of the root sys- 
tem was similar to that found at the second examination, except that it was 
somewhat more extensive. The first 8 or 9 inches of soil were filled with a 
mass of finely branched roots, many of which extended only a few inches, but 



10 



Development and Activities of Roots of Crop Plants. 



others as far as 1.4 feet from the base of the plant. Thus, the spread of these 
shallow roots had increased 4 or 5 inches since May 29. These horizontal 
roots often continued their course near the surface of the soil. Frequently, 
throughout their whole length, no portion of them could be found that was 
deeper than 1.5 to 3 inches. Other roots extended almost parallel with the 
surface for a distance and then turned downward, ultimately reaching depths 
of 1 to 5 feet. Still others descended almost vertically until they reached 
depths of 5 to 5.5 feet or more, the maximum length found being 6.7 feet 




Fig. 1. — A. Root system of University No. 21 oats 59 days old. 
B. Swedish Select oats 60 days old. 



(fig. 2 a). 5 to 7 of these deeper roots were commonly found. This is an 
increase of 4 or 5 over those present at the time of the preceding examination. 
The roots were all profusely branched with fine branches ranging from 0.1 to 
4 inches in length. This was especially true of those lying near the surface, 
where the branches were longest. On practically all of the roots at this 
time the branches extended almost to the tips. The roots were very fragile, 
especially the deeper ones. The shrunken and shriveled cortex indicated 
that considerable material had been transported from them. The soil was 
fairly well filled with roots to a depth of 3.8 feet, and below this to 5.4 feet 
they were quite numerous. Thus, it is evident that the root system of this 



Investigations at Peru, Nebraska. 



11 



oat is splendidly adapted not only for absorption in the surface soil, but also 
at much deeper levels. This extensively developed root system undoubtedly 
plays no small part in making this strain of Kherson oats one of those best 
adapted to the semiarid condition of Nebraska. 

Growth conditions during June were very favorable. The mean day and 
night temperatures were 74° and 64° F. respectively. The mean tempera- 
ture of the first 3 feet of soil was 74.6° F. The rainfall was 4.3 inches, while 
about 56 per cent of the days were cloudy. Hence the relative humidity was 
rather high. The average daily evaporation for the month was 24 c. c. 
Water-content determinations on June 23 and 28 showed a margin of about 
6.5 per cent above the hygroscopic coefficient in the first 3 feet of soil. Except 
for clear, dry weather during the last 10 days of this period, conditions were 
such as to stimulate a very luxuriant vegetative growth. However, the 
plants stood up well till the grain was ripe. The yield was at the rate of 
62.5 bushels per acre. The yields of the small cereals were based upon the 
yield by weight of a single square rod selected from a representative portion 
of each plat. 

Swedish Select Oats, Avena sativa. 

The root system of the seedling stage of this plant was studied on April 19, 
19 days after the seed had been planted. Each plant had a single leaf about 
1.5 inches long, which had been above ground about 9 days. 3 or 4 roots 
grew out from the hypocotyl. One of these, although not unlike the others 
in general appearance, took a downward course similar to that of the tap-root, 
reaching a depth of 10 inches. The other roots, which were 1 to 5 inches in 
length, descended more obliquely. The roots were about 1.5 mm. in diam- 
eter, entirely unbranched, but densely covered with root-hairs. They main- 
tained such an intimate contact with the soil particles that no portion of 
the excavated root was visible, except the very tips, upon which root-hairs 
had not yet developed. Environmental conditions of the several intervals 
of growth have already been given in the discussion of University No. 21 oats. 

The root system was again examined 60 days after planting. The crop 
had reached a height of 10 to 12 inches, and the number of stalks, including 
tillers, varied from 1 to 4 per plant. The roots originated both from the old 
kernel and from a node just below the soil surface. Most of the roots either 
pursued a course almost vertically downward or ran off obliquely to a dis- 
tance of 6 to 10 inches and then turned downward with a long, graceful 
curve (fig. 1b). A few were short and ran almost parallel with the soil 
surface, where their ramifications terminated 6 to 10 inches from the base of 
the plant. The deeper roots penetrated to depths of 3.2 to 3.5 feet, with a 
maximum of 3.7 feet. The roots to within about 8 to 12 inches of the tip 
were copiously branched. These branches varied in length from a few milli- 
meters to 5 or 6 inches and the relative number of the longer branches was 
unusually large. The laterals of the first order were in turn often branched 
and rebranched. The deeply penetrating roots were usually from 4 to 6 
in number, while shallower ones varied from 4 to 7, or even more. 

The last investigation of the underground parts of this plant was made 
July 2. This was 93 days after the seed had been planted and when the crop 
was beginning to ripen. Each plant had from 1 to 3 stalks, with an average 



12 



Development and Activities of Roots of Crop Plants. 



height of about 3 feet. The mature root system bore a strong resemblance 
in form to that found at the last examination. It was characterized by the 
large number of deeply penetrating roots. Some of these ran almost verti- 
cally downward from the base of the plant, while others went out obliquely 
to a distance as great as 12 inches and then turned downward with a gradual 




Fig. 2. 



-A. University No. 21 oats at maturity. 
B. Swedish Select oats at maturity. 



curve. Other roots took positions intermediate to these extremes (fig. 2 b). 
The number of these deeper roots varied from 7 to 11. They pursued a 
rather tortuous course. The usual depth of penetration ranged from 2 to 



Investigations at Peru, Nebraska. 



13 



6 feet or more, while the maximum depth was 6.8 feet. The soil was well 
filled with these roots to a depth of 4.6 feet; many reached depths of 5.5 to 
5.8 feet below the surface. They were profusely branched to the second 
order; the length of the branches varied from 0.3 to 5 inches. The last 6 to 
8 inches of the roots were unbranched. 

The superficial system was composed of much finer roots, which ran nearly 
parallel with the surface or took a slightly oblique course. The longest of 
these were from 1 to 1.3 feet. They were profusely branched and rebranched 
with fine rootlets, which extended in all directions from the main root. 
Branches of the first order were sometimes 4 to 5 inches long. In many 
instances their ends were found just below the dry, dusty surface of the soil. 
The shallower roots were developed only to a moderate degree at the second 
examination, but as the time of maturity approached this portion of the root 
system continued to grow and extend its area markedly. At no time, how- 
ever, did its extent and density even closely approximate that of the Uni- 
versity No. 21 variety (c/. figs. 1 and 2). 

Summarizing, this oat is characterized by a well-developed, deeply pene- 
trating and profusely branched root system. The depth of penetration of 
so many of the larger roots may be correlated with the luxuriant growth of 
tops. This brings about a balance between absorption and transpiration. 
This oat grew rank and produced heavy straw. The plat yielded at the rate 
of 40 bushels per acre, but the quality of grain was only fair, because of the 
presence of many light kernels, due in part to an attack of Puccinia graminis 
avence. 

Durum Wheat, Triticum durum. 

The first examination of Durum wheat was made 19 days after sowing. 
The plants had been above ground about 9 days and had but one leaf un- 
folded. They were approximately 3 inches tall. The root system consisted 
of 4 or 5 roots, usually 5, which ranged in length from 1.5 to 8 inches. While 
some in their descent made only small angles with the vertical, most of them 
pursued a more oblique course downward, and, compared with their length, 
spread rather widely from the base of the plant. In some instances the tips 
of the roots were 4 or 5 inches from the vertical. Secondary branches vary- 
ing from 2 to 8 in number had begun to appear on some of the older roots 
along the first 1 to 1.5 inches of their course. They looked like tiny white 
threads only 2 to 3 mm. long. They were rather tough in texture and, with 
the exception of the extreme tips, fairly well covered with root-hairs. 

The second excavation was made on May 30, 60 days after the date of 
planting. The crop was from 8 to 12 inches high, and each plant had from 
1 to 4 shoots. The roots were extremely fine and fibrous and showed more 
or less distinctly two types— a surface-feeding type and a deeper absorbing 
one. Regarding the latter, it is of interest to note that Robbins and Rot- 
mistrov are not in accord as to their point of origin. In discussing the pri- 
mary roots that spring from the region of the hypocotyl, Robbins (1917 : 91) 
states: "This whorl constitutes the primary or temporary root system. It 
usually dies before the plant is full grown." Rotmistrov (1909 : 32), in 
referring to the smaller cereal crops in general, says: " These primordial 
rootlets continue to be main roots or roots of the first order during the whole 
period of vegetation which follows." 



14 



Development and Activities of Roots of Crop Plants. 



The root systems of the wheat plants examined agreed with the statement 
of Rotmistrov, for not only at this period did these primary roots penetrate 
deepest, but they lived and continued to grow and function until the plant 
matured, at which time they had reached greater depths than any of the roots 
that formed later (fig. 3 c). Of these primary roots a few grew almost ver- 
tically downward, but by far the greater number passed off obliquely to a 
distance of 0.5 to 1.3 feet and then, turning downward, pursued a zigzag but 
generally vertical course to a depth of 3.9 to 4.2 feet. The maximum depth 




Fiq. 3.— A. Marquis wheat 20 days old; B. 70 days old. C. Durum wheat 60 days old. 



of penetration was 4.5 feet. These main roots were yellowish in color and 
quite tough. Throughout their course, excepting the last 8 to 12 inches, 
they were quite abundantly branched, the branches varying from a few milli- 
meters to 2 or more inches in length. These branches were themselves often 
rebranched. Just below the surface of the soil another set of roots arose 
from a node on the main stalk. These passed out almost horizontally in 
all directions to a distance of 6 to 8 inches. Some of these, however, were 



Investigations at Peru, Nebraska. 



15 



just beginning to push out from the node, while between these extremes 
roots of all intermediate lengths were found. They were fairly well branched 
to the second order; the branches extended in all directions and ranged from 
0.2 to 2 or 3 inches in length, according to their age. 

A final root examination was made July 4, 95 days after the wheat had been 
drilled. The plants were 2.2 to 2.8 feet high and averaged two stalks each. 
The grain was in the stiff-dough stage and the heads had begun to turn 
yellow. Relative to the other smaller cereals, this plant had a rather meager 
surface-feeding system at maturity. Usually this consisted of 6 to 8 (rarely 
more) roots that extended out in an almost horizontal direction (fig. 4 a). 
They varied in length from 2 to 14 inches and ended only 4 to 7 inches below 
the surface. They were fairly well supplied with rootlets to the second and 
third orders. The primary roots, as determined at the previous examination, 
continued to be the most pronounced portion of the root system. From 
their points of origin they ran either vertically downward or downward and 
outward until they reached a distance of 0.4 to 1.3 feet from the vertical, 
where they turned downward, pursuing a more or less zigzag course. A few 
of the roots which originated from the node above the old kernel, and which 
at the second investigation had a course more or less horizontal, had now 
turned downward and penetrated deeply. All the roots were well supplied 
with branches from a few millimeters to 3 or 4 inches or more m length. 
These laterals were rebranched. The soil was especially well filled with 
roots to the fourth foot; many also occurred in the fifth and sixth foot, and 
not a few extended even deeper. The maximum depth to which roots ex- 
tended was 7.4 feet. Due to an attack of stem rust (Puccinia graminis 
tritici), this wheat yielded at the rate of only 8 bushels per acre. Moreover, 
there were many shriveled kernels, which made the gram of rather inferior 

^Durum wheat, when grown under the conditions described, has a surface 
root system of only medium extent, but a large, extensive portion which 
penetrates very deeply. These studies show clearly, moreover, that the root 
system develops coordinately with the above-ground parts, for it is only m 
this way that the increasing demands of the developing shoot for water can 
be successfully met. 

Marquis Wheat, Triticum ^stivum. 
The roots of this plant were examined April 25, 20 days after planting. 
Most of the plants had shown above ground for about 9 days. The tops 
were 2 to 2.5 inches high and the second leaf had just begun to unfold. Three 
or four roots had developed. Their courses varied widely. Some had grown 
almost straight downward, others diverged at wide angles from the vertical, 
while still others had taken an intermediate position with reference to these 
extremes (fig. 3 a). The number of roots varied from 3 to 5, but most of 
the plants had 4. The maximum spread from the vertical was 7 inches; 
the greatest depth of penetration was 11 inches. The roots ranged m length 
from 5 to 9 inches. They were fight in color, had a diameter of a millimeter 
or less, were rather tough, and all their surface, excepting the very tip, was 
covered with a copious growth of root-hairs. For a distance of 2 to 3.5 
inches from the base of the longer roots, branches had begun to appear. 
The longest of these, however, did not exceed 0.5 inch. 



16 



Development and Activities of Roots of Crop Plants. 



Root development was again determined on June 14, 70 days after the 
crop had been planted. The wheat was 1.5 to 2 feet tall and the stems had 
begun to joint. Each plant had from 2 to 4 stalks. The root system was 
characterized by a shallower portion, consisting of 9 to 14 roots, which 




Fig. 4. — A. Durum wheat at maturity. 

B. Marquis wheat at maturity. 



originated from the nodes of the stalks below the soil surface. These roots 
ran horizontally, or very nearly so, to a distance of 3 to 10 inches from the 
base of the plant. They ended from 2 to 8 inches below the surface. They 



Investigations at Peru, Nebraska. 



17 



were fairly well branched to the second order with delicate branches that 
extended in all directions and formed a network (fig. 3 b). 

The part of the root system which penetrated deeper consisted of 3 to 5 
roots. They originated very near the old kernel. Some of them ran almost 
straight downward to a depth of 4.8 to 5.5 feet. The maximum depth was 
5.8 feet. Others wandered off rather obliquely to a distance of 0.6 to 1.3 
feet and then took a vertically downward course. These roots that spread 
more widely did not penetrate so deeply, but ended at the 2.5 to 4.5 foot 
level. All portions of the deeper roots, except the last 6 to 8 inches, were 
well supplied with fine, often rebranched laterals. The soil was fairly well 
filled with these main roots and their branches to a depth of from 4 to 

4.6 feet. 

The last examination was made on July 7, 93 days after the planting. 
The height was from 2.5 to 2.8 feet, and the plants averaged about 2 stalks 
each. The grain was in the stiff dough and the heads had just begun to 
ripen. The shallower portion of the root system was not markedly devel- 
oped; in fact, scarcely more so than at the preceding examination on June 14. 
It consisted of 9 to 14 roots that took their origin from nodes on the stalk 
below the soil surface. These either extended laterally quite parallel with 
the soil surface or took a downward and outward course, thus extending in 
all directions from the base of the plant. They varied in length from 0.2 to 

1.7 feet (fig. 4 b). While they were quite well supplied with branches from 
a few millimeters to 3 or 4 inches long, these were not copious. The longer 
laterals frequently rebranched. The roots that penetrated deeply, usually 
from 3 to 8 in number, either ran vertically downward from the old kernel or 
at a depth of 4 to 6 inches took a course obliquely outward to a distance of 
4 to 16 inches and then turned downward. Of these roots there were gen- 
erally one or two more than at the time of the second examination. They were 
well supplied with branches, except the last 8 to 14 inches, where laterals 
occurred only rarely or not at all. These branches varied in length from 
1 mm. to 2 or 3 inches. The diameter of the main roots was approximately 
1.5 mm. The soil was well filled with these roots and their branches to a depth 
of 3.7 to 4.2 feet. Roots were frequent even at a depth of 5 feet, while 
some reached a maximum depth of 6.7 feet. 

A survey of these data shows that, while this wheat is provided with a 
root system fitted to absorb both in the surface as well as in the deeper soil, 
under the conditions of growth in this experiment the shallower portion was 
not highly developed. The number and extent of the longer roots, together 
with their great depth of penetration, is a marked feature and is especially 
impressive when the extent of the underground parts is compared with 
height of tops. The yield of Marquis wheat was at the rate of only 3.7 
bushels per acre. It was planted a week later than the Durum wheat and 
was somewhat more susceptible to the epidemic of stem rust which swept 
over much of the Missouri Valley in the summer of 1919. The plants were 
attacked just before blooming, and by the time the grain was going into the 
dough stage the surface of the leaves and stems was covered with rust pus- 
tules. This resulted in very light, shriveled kernels. 



18 Development and Activities of Roots of Crop Plants. 

Manchubia Barley, Hordeum vulgare. 

The barley roots were examined the first time April 25, 20 days after the 
seed had been drilled. The plants had shown above ground about 8 days. 
They averaged 5 inches in height and the second leaf was just beginning to 
unfold. In this early state of growth, however, the root system showed a 
marked tendency to develop into two rather distinct portions. One set of 
roots grew at once toward the subsoil, while the other ran off quite hori- 
zontally. Of the former lot there were two or three on every plant. Quite 
regularly one of these, not unlike the others in structure or general appear- 
ance, took a course so vertically downward as to constantly remind one of 
a tap-root. The others, while nearly always growing rather straight down- 
ward, occasionally wandered off in an oblique direction to a distance of 6 to 
9 inches from the perpendicular and finally reached a depth of 0.7 to 1.2 
feet. Small branches had appeared on the older portions of the roots to a 
distance sometimes as great as 4.5 inches from the base of the plant. The 
branches did not exceed 0.5 inch in length. 

The other portion of the root system consisted of four or five roots which 
usually took an almost horizontal course through the soil. Occasionally 
one or two of these even curved up slightly towards the surface. Many 
reached a length of 4 to 8 inches and ended only 3 or 4 inches below the soil 
surface. This portion of the root system was also branched quite sparingly. 
However, the branches occurred to within an inch of the root-tips. The roots 
were a millimeter or less in diameter, light in color, rather elastic, and quite 
well covered with root-hairs to within a short distance of the tip (fig. 5 a). 

The second examination was made on May 29, 54 days after planting. 
The number of stalks per plant, including tillers, varied from 2 to 4. The 
height ranged from 9 to 12 inches. Barley, as was true of all the small 
cereals at the time of the second examination, had thrown out roots from two 
distinct points, the original ones from the hypocotyl and the second group 
from a node just below the surface of the soil. The shallower and deeper 
portions of the system already noted were still maintained (fig. 5 b). The 
roots composing the former extended out almost horizontally in all directions 
from the base of the plant, or had only a slightly downward course. In 
number they ranged from 8 to 12, were from 5 to 16 inches long, and ended 
from 2 to 10 inches below the surface of the soil. These shallower roots 
were profusely branched and rebranched to the second and third orders 
with thread-like branches varying from a few millimeters to 3 or 4 inches 
in length. The first 6 to 8 inches of soil were densely filled with these hori- 
zontal roots and their network of branches. 

The second type of roots penetrated deeply. Two to four occurred on 
each plant. The depth of penetration was usually from 3.7 to 4.2 feet, 
although some reached the 4.5-foot level. These main roots frequently took 
a vertical course, but as often wandered obliquely from the base of the plant 
to a distance of 8 to 10 inches and then ran irregularly downward. These 
roots were profusely branched within the first 3 feet of soil; sometimes as 
many as 20 branches occurred on a single inch. The last 6 to 8 inches were 
not branched. The old roots near the base of the plant were hard, wiry, 
and yellowish in color, while the new ones were crisp and white. None of 
them, at this point, were more than 1 mm. in diameter. As a rule, the diam- 



Investigations at Peru, Nebraska. 



19 



eter of the younger portions was somewhat greater, due to their greater 
succulency. 

The mature root system of barley was studied on June 28, when the plants 
were 84 days old. The crop was from 2 to 2.5 feet high and each plant had 
2 to 3 stalks bearing heads. The crop was ripening rapidly and was harvested 
5 days later. It yielded grain of good quality at the rate of 25.8 bushels 
per acre. The shallower portion of the root system was practically the 



1 




















peg- 












3 


A 




A 










B 


T 1 





Fig. 5. — A, Manchuria barley 20 days old; B. 64 days old. 



same as at the time of the second examination on May 29. The greater 
part of it originated from the stalk above the old shrunken kernel and spread 
out horizontally at a depth of 2 to 10 inches below the soil surface. These 
roots varied from 0.1 to 1.3 feet in length. They were rebranched only to a 
moderate degree. 

The primary roots that took their origin from the hypocotyl constituted 
the part which penetrated deeper. However, there were some exceptions. 
Occasionally a root which had developed later from the node on the stem 



20 



Development and Activities of Roots of Crop Plants. 



turned downward and penetrated deeply into the subsoil (fig. 6). Some of 
the roots, just described, descended almost vertically, others ran obliquely 
outward 0.3 to 1.3 feet and then took a perpendicularly downward course. 
The soil was fairly well filled with roots to a depth of 3.7 to 4.2 feet, while 




Fia. 6. — Manchuria barley at maturity. 



many penetrated to a depth of 5 to 5.8 feet. The maximum penetration 
was 6.3 feet. The roots were 1 to 1.5 mm. in diameter. They were all 
abundantly supplied with branches from 0.2 to 2 or 3 inches in length. The 
branches now extended quite to the root-tips ; showing that growth was 
complete. 



Investigations at Peru, Nebraska. 



21 



Corn, Zea mays indentata. 

The corn plat was plowed April 4 to a depth of 4 inches and harrowed 
immediately afterward. It was harrowed again May 5 to keep it free from 
weeds, and on May 9 was planted with Iowa Silver Mine corn. This is a 
large, rather late maturing variety. Before planting, the plat was marked 
off in rows 3 feet apart and the seed was drilled along the marks without 
furrowing. The kernels were planted 3.5 inches deep and 1.4 feet apart in 
the rows. That part of the plat in which the excavations were made was 
cultivated very shallow with a hoe so as not to disturb the roots. It was 
hoed three times, on May 31, June 16, and July 9, respectively. 

The first examination of the root system was made June 14, 36 days after 
planting. The height of the crop averaged from 10 to 14 inches and the 
seventh and eighth leaves were just unfolding. The stand was very uniform. 
In this early stage of growth it has a distinctive surface system of roots. 




Fig. 7. — Root system of Iowa Silver Mine corn 36 days old. 

Of the several plants examined no root approximating the position of a tap- 
root was found. Whether originating from the hypocotyl or from a node 
above, the roots took a course parallel or almost parallel with the surface 
of the soil. In this manner they ran out in all directions from the points 
of origin. The number of roots varied from 10 to 15; they were about 1.5 
mm. in diameter, and ranged in length from 0.1 to 2.6 feet. They ended 
from 0.2 to 1.3 feet below the surface (fig. 7). Throughout their length, 
excepting the last 8 to 12 inches, all the roots were profusely branched and 
as many as 33 rootlets were counted on a single inch. The branches varied 
from a few millimeters to 4 inches in length and were themselves rebranched. 

*This period had been very favorable for plant growth. Although May was 
somewhat dry, the precipitation during the first half of June was greater 
than normal. The available water-content to a depth of a foot averaged 



22 Development and Activities of Roots of Crop Plants. 

12 per cent. The soil was in fine tilth and warmed up rapidly. The average 
soil temperature to a depth of 1 foot was 63° F. The above-ground condi- 
tions were also favorable. The mean daily temperature was about 64° F. 
The last half of May was clear and dry and the first half of June was cloudy, 
but warm. The daily evaporation for the period in May was 24 c. c, but 
for June, due mostly to cloudiness and an increased humidity, it dropped to 
20 c. c. Thus, the environmental factors, both aerial and within that part 
of the soil occupied by the roots, were conducive to rapid growth. The corn 
plants responded favorably to these conditions, as shown by the fact that 
within a period of 36 days from the date of planting they had reached an 
average height of 12 inches. 

The second examination of the corn roots was made July 5, 57 days after 
planting. The stalks were about 4 feet tall and 4 or 5 nodes were visible 
(plate 1 a). During the period intervening between the first and second 
excavations, a remarkable extension of the root system had taken place. 
It now consisted of two rather distinct portions. One of these comprised the 
original roots, together with those of later development scattered among 
them and which arose from nodes at very short intervals just above the old 
kernel. These roots ran out either horizontally or descended very gradually, 
extending laterally to a distance of 2 to 4 feet from the base of the stalk, where 
they usually turned downward rather abruptly (fig. 8). They penetrated 
to a depth of 1.5 to 4.6 feet. The other portion of the root system consisted 
of a large group of roots of later development that ran almost vertically 
downward or spread out only a short distance from the base of the plant and 
then took a downward course. The spread of these roots was seldom more 
than 10 or 12 inches from the vertical. They were the youngest roots, 
growing vigorously, and were found in all stages of development. Some 
were just starting from the base of the plant, while others had already pene- 
trated to a depth of 4.7 feet. They were succulent and turgid and had a 
diameter of 3 or 4 mm. or more. Both groups of roots were well supplied 
with branches, those lying near the surface were most profoundly branched. 
These branches were in turn often branched and rebranched to the third 
and fourth orders. The longer branches were confined to the first foot of 
soil and, with their many ramifications, formed a wonderfully dense and 
efficient surface absorbing portion of the system. Below the first foot the 
branches from the main roots were shorter, usually not exceeding 4 or 5 
inches. In color the roots were either brown or white, depending upon their 
age. The last 6 to 12 inches of the growing tips were pearly white and devoid 
of branches. 

This period was more favorable for growth than the preceding. Both 
air and soil were constantly growing warmer. The mean daily air-tempera- 
ture was 75° F. The soil-temperature, taken for the first 8 days of the period 
only, reached 76.3° F. as an average for the first 3 feet by June 23. This was 
11° F. higher than the reading of June 9. The precipitation was about nor- 
mal, and the first 3 feet of soil had an average available water-content of 

13 per cent. 60 per cent of the days were clear. The mean daily evapora- 
tion was 25 c. c. The crop responded to these highly favorable conditions 
for growth in a remarkable manner. Although the period was but 21 days 
in length, the corn increased its height approximately 3 feet, an average 



24 Development and Activities of Roots of Crop Plants. 

daily growth of 1.7 inches. The plants were sturdy and bore an abundance 
of dark-green leaves. 

The root system of the maturing corn plants was examined September 2, 
116 days after planting. The stalks were 8 to 9 feet high and, while a few 
of the leaves had died, most of them were still green. The husks on the 
ear were just beginning to dry and the kernels were dented (plate 1 c). The 
shallow portion of the root system had scarcely increased over that found 
at the July examination, when the plants were 57 days old (cf. figs. 8 and 9). 
Most of the roots of this type were found within the first foot of soil, running 
in all directions from the base of the plant. Some of them maintained a 
horizontal position throughout their entire course, which sometimes reached 
a length of 4 feet. Others ran off at various angles to distances varying from 
a few inches to as much as 3.7 feet and then turned downward either abruptly 
or with a gentle curve. They then pursued their irregular course downward 
to a depth of 2.5 to 3 feet. This surface portion of the root system was 
profusely branched to the second and third order with branches ranging 
from less than an inch to 2 feet in length. The surface soil to a depth of 8 
to 12 inches was literally filled with these fine rootlets. 

Unlike the shallower portion of the root system, the more deeply pene- 
trating part had made a most marked development. On July 5 its growth 
had just well begun, but by September 2 it had made a really remarkable 
development. The number of these more vertically penetrating roots varied 
from about 20 to 35. They either ran straight downward from the base of 
the plant or obliquely outward to a distance of 2 feet or more, and then with 
a graceful curve took the perpendicular line of growth. Of these roots a 
few were short and did not grow deeper than 1 or 2 feet; many reached a 
depth of 7 feet, while still others were deeper. The maximum depth of pene- 
tration was 8.2 feet. At the point of origin these roots were 2 to 5 mm. in 
diameter. They were all profusely branched with laterals varying from less 
than an inch to 1.3 feet in length. It was not unusual to find 10 or 12 of 
these branches on an inch of the main root. The longer laterals were 
rebranched. 

The period intervening between the second and final examination was 
extremely dry and hot. During the whole interval of approximately two 
months, the precipitation was only about 2.5 inches, which, with one excep- 
tion, fell in showers so light as to be of very little value to the crop. The 
exception was August 25, when the precipitation measured slightly over 0.75 
inch. 70 per cent of the days were clear. The average daily temperature 
for the period was about 82° F. and on several occasions temperatures of over 
100° F. were recorded. Due in part to the low humidity accompanying 
these conditions, the daily evaporation was high. Until July 22 it averaged 
only 24 c. c, but for the next two weeks interval it reached an average of 
41 c. c. daily. Because of these drought conditions the available soil-mois- 
ture became greatly depleted. During the part of the period in July the 
average available water-content for the first 3 feet was 8.7 per cent. On July 
29 the fourth and fifth foot of soil had 12 per cent. During August water- 
content was greatly reduced, the average for the first 3 feet being only 5.6 per 
cent. On September 2, when the roots were finally excavated, the soil to a 
depth of 5 feet had only 3.5 per cent of available moisture. The dry soil was 




Fig. 



Investigations at Peru, Nebraska. 



25 



a factor in causing the crop to mature somewhat prematurely and resulted in 
a heavy reduction in yield. The plat averaged only 37 bushels per acre. 

Summarizing, the shallower part of the root system was extensive and 
completed its development early, so far as lateral spread is concerned. 
The group of roots which penetrated deeper developed later and continued 
to increase in number and extent practically until the time of maturity. 
The lateral spread on all sides of the plant was approximately 4 feet and the 
maximum penetration was 8.2 feet. Thus, corn is furnished with a remark- 
ably extensive and efficient root system. 

Earlier Investigations of Corn. 

With a few exceptions, most of the investigations of corn roots have been 
carried on in connection with tillage experiments. Sturtevant (1882) 
traced corn roots at the New York Agricultural Experiment Station to a 
depth of 2.5 feet. He states that corn plants for that year produced 1,000 
roots in the first 4 inches of soil to 1 root produced below that depth. Beck- 
with (1885) working at the same station, found that the lateral roots reached 
a distance of 3.7 feet on all sides of the plant, and that, while a few roots were 
traced to a depth of 2.5 feet, the majority of them reached a depth not greater 
than 1.4 feet. Goff (1887) covered the fertile soil in which corn was growing 
with a 12-inch layer of infertile soil. The corn roots grew horizontally at 
the upper surface of the fertile soil, but did not penetrate upward into the 
layer of infertile soil. From this he decided that " abundant food and mois- 
ture are more essential to the development of corn than a high soil tempera- 
ture." Hickman (1887) stated that corn grown in a stiff clay loam in Penn- 
sylvania "seemed to be a shallow rooted plant." He further observed that 
"nodal roots, especially those later formed, branched out horizontally from the 
stem for a considerable distance and then turned down quite rapidly." 
Hays in 1888, working at St. Paul, Minnesota, got results which indicated 
that corn roots, under his conditions, grow mainly near the surface if there 
is a good supply of moisture in these layers, but in time of drought they tended 
to grow deeper and extend shorter distances horizontally. The same investi- 
gator (1889), by excavating the roots of corn planted several feet apart, 
found that they at first grow horizontally because the surface soil is warm, 
the upper soil is rich in plant food, and contains an abundance of moisture. 
He further found, after about the fourth week, that both the primary roots 
and those from the nodes as well take a downward course, the latter from 
their very beginning. This investigation was carried on in a rather dry 
season in "drift" soil only fairly retentive of moisture. 

King (1892) at Madison, Wisconsin, found that corn roots grow 4 feet 
deep and in well-drained soil exceed this depth, and also stated that at tassel- 
ing time "the roots have fully occupied the upper 3 feet of soil in the entire 
field." Ten Eyck (1904), by washing out the roots of Kansas Sunflower 
corn 60 days after planting, at Manhattan, Kansas, found the soil to be filled 
with roots to a depth of 2.5 feet, while some reached a depth of over 3 feet. 
He further observed that there were two classes of roots found, namely, 
"those that curve out from the crown and strike more or less directly down- 
ward into the soil" and "those that spread out from the root-stem in a hori- 
zontal plane," then "curve more or less abruptly downward, often ending 



26 



Development and Activities of Roots of Crop Plants. 



2 to 3 feet beneath the opposite hill." The corn in this case was level-planted. 
In examining the mature corn 125 days after planting, the stalks were 8 feet 
high, the roots "had reached a depth of fully 4 feet, and some were traced to 
the depth of 5 feet." Shepperd (1905), at Fargo, North Dakota, concluded 
that "corn roots commonly reached a depth of 3.5 to 4 feet, as is shown by 
root experiments covering a period of 5 years." Miller (1916) grew Pride of 
Saline corn at Garden City, Kansas, in sandy-loam soil, irrigated in the fall 
with 8 to 10 inches of water after plowing. The corn grew in alternate rows 
with Blackhull kafir and Dwarf milo respectively. The roots were excavated 
by washing. During the wet season of 1915 they were found to penetrate 
6 feet deep and to have a lateral spread of 3.7 feet from the base of the plant. 
During the dry season of 1914, when but approximately one-third as much 
precipitation occurred during the growing-period of the plants, the depth of 
penetration was the same, but the horizontal spread was 8 inches less. The 
tops reached a height of 7 feet in 1915, but in 1914 they did not exceed 6 feet. 

Investigations of corn roots in the United States have been rather limited 
in extent. In most cases, too, they are somewhat unsatisfactory in regard to 
the conclusions reached. In fact, except for the work of Miller, this review 
shows no results in respect to the lateral spread and depth of root penetration 
comparable to those obtained at Peru. 

Other investigators give data on root extent that are greatly at variance 
with those found in our studies. These discrepancies may be due in part to 
varietal and environmental differences, but it is also probable that they may 
also be attributed in part to incomplete and faulty methods of excavation. 
Indeed, some of the workers state frankly that the roots were badly broken 
in the process of separating them from the soil by washing and also in some 
cases that the roots were not traced to their extremities. 

With reference to the order of root development, our observations coincide 
very closely with those of Hays, namely, that the first roots grow horizontally 
and that later both these primary roots and those from the nodes as well 
take a downward course, the latter from the very beginning. He stated that 
this change in direction of growth began about the fourth week. At Peru, 
however, it came later. Even 5 weeks after planting there was no indication 
of this downward course on the part of the roots. Moreover, the lateral 
roots had not yet reached the limit of their spread by approximately 2 feet. 
Hickman and Ten Eyck also noted the later downward turn of the horizontal 
roots. 

Potato, Solanum tuberosum. 
The plat in which the potatoes were grown was plowed April 4 to a depth 
of 6 inches and immediately harrowed. The next day the ground was fur- 
rowed out with a plow into rows 3 feet apart and planted. In preparing 
the cuttings the tubers of Early Ohio potatoes were cut so that each piece had 
from two to three buds, and then all the buds but one in each piece were 
excised. In this way each hill had but one plant. The pieces of tubers were 
placed 2 feet apart in the row and were covered to a depth of 3 inches. On 
May 5 the potatoes, which were just coming through the ground, were har- 
rowed to level the surface and kill the weeds. On May 31 and again on June 
16 they were hoed with a garden hoe. Each hoeing was shallow in order to 
kill the weeds but not to disturb the potato roots lying near the surface. 



Investigations at Peru, Nebraska. 27 

The potato was examined only twice. The first examination was made 
May 31, 56 days after planting. The tops were 9 to 12 inches high. At this 
time the root system was almost entirely near the surface. As many as 55 
roots took their origin from the base of a single plant and ran off practically 
parallel to the surface of the soil. They varied from a few inches to 2.2 feet 
in length. None penetrated deeper than 1.5 feet and with few exceptions 
were throughout their length within the first 8 inches of soil. The earth about 
the plants was so thoroughly filled with these roots that it was found impos- 
sible to represent all of them in one plane. Consequently the drawing 
(fig. 10) shows but one-half of the entire root system. 

Some of the roots were confined to the first 2 inches of soil. As is shown 
in figure 10, a number of the deeper roots had a tendency to turn quite ab- 
ruptly downward. A dry period of short duration occurred at this time, and 




Fig. 10. — One-half of root system of a potato plant 56 days old. 



it was uncertain whether this downward turn was normal or whether it was 
a response to low water-content of the surface soil. The dry weather may 
have had some influence, but subsequent investigation indicated conclusively 
that this habit of growth is normal. The main roots were densely covered 
with thread-like branches from a few millimeters to 3 or 4 inches in length. 
So numerous were these capillary branches that the soil to the very surface 
was thoroughly penetrated by them. Several young potatoes from 0.3 to 
2 cm. in diameter had formed. 

This period, excepting the last part of May, had been rather unfavorable 
for growth, because of cool weather. The soil-temperature to a depth of 
2 feet averaged but 55.1° F. This was due in part to the high water-content 
of the soil resulting from the heavy April precipitation. At no time, within 



28 Development and Activities of Roots of Crop Plants. 



the layer occupied by the roots, did the available moisture fall below 11 
per cent. Beginning with April 21, when the atmometers were installed, the 
daily evaporation averaged but 18 c. c. per day. During the last days of May, 
however, more favorable growth conditions ensued, and the plants passed 
into the next period under circumstances conducive to rapid development. 

The final examination was made on July 8, 94 days after planting, when 
growth was complete and about one-third of the leaves were dead (plate 1 b). 
One-half of the mature root system is shown in figure 11. The root system 
was very unlike those of the cereals, in that there was an almost entire ab- 
sence of roots penetrating vertically downward from the base of the plant. 




Fig. 11. — One-half of root system of a mature potato plant. 



In form it was almost identical with that found in the earlier stage of its 
development. Practically the only difference was in its extent. With a few 
exceptions, the roots extended outward and downward until they reached 
a distance of 0.5 to 2.1 feet from the vertical and a depth of 0.7 to 1 foot 
from the surface. They then turned more or less abruptly downward and 
continued their irregular course to a depth of 2 to 4.7 feet. A few roots 
extended out almost horizontally at a depth of 2 or 3 inches to a maximum 
distance of 15 to 20 inches, but did not turn downward at that point. All 
these roots, including both the shallow and deep ones, were freely branched 
throughout their course, even to their very tips, with fine white branches 



Investigations at Peru, Nebraska. 



29 



from 0.5 to 4 inches in length. Infrequently, longer branches were found 
near the surface, which sometimes had an extent of 1.3 feet. All of the lat- 
erals were frequently rebranched. It should be noted in this connection 
that the individual plants were quite variable, both in respect to the size of 
the tops and the number and extent of the roots. 

This period was rather warm, with a slight excess of cloudiness and 
humidity. The mean daily temperature was 75° F. and the average daily 
evaporation 23 c. c. The rainfall for June, although nearly normal in 
amount, was not well distributed, over half of it falling during the first four 
days of the month. However, the plants did not lack water. On June 28 
the available moisture to a depth of 5 feet was 11 per cent. The plants did 
not recover entirely from the retardation in growth which they underwent 
during the dry, cold month of May. This resulted in a yield of only 2 or 
3 tubers per plant, and these were of small size, averaging not over 2 or 3 
inches in diameter. The whole plat yielded at the rate of only 32 bushels per 
acre. 

In its early growth the potato had a distinctly superficial system of roots. 
After extending out horizontally to a distance of 1 to 2,2 feet or more, these 
same roots then turned more or less abruptly downward and formed the 
deeper penetrating portion of the system also. This left the subsoil area 
directly below the plant practically free from its own roots. The individual 
plants were more variable, both in respect to the size of the top and the num- 
ber and extent of the roots than were any of the monocptyledonous crops. 

Earlier Investigations of Potatoes. 

Few investigations on the root development of potato are found in a 
survey of the literature. Beckwith (1885) reported that at the New York 
Experiment Station roots of the White Star potato reached a maximum depth 
of 1.6 feet and that the horizontal roots were traced to a distance of 2.2 to 
2.5 feet from the base of the plant. He concluded that most of the roots 
lay within the first 1.2 feet of soil. Ten Eyck (1899) at Fargo, North Dakota, 
working with Early Ohio potatoes, stated that the roots during 1898 were 
few in number and did not penetrate deeply. He washed the roots out of 
the soil with a jet of water on September 13, at a time when they were partly 
decayed and, as he states, they made a "bad mess." In 1899 he examined 
the Rural New Yorker No. 2 potato at the same station and concluded that 
late-maturing potatoes, of which this variety is an example, "root more 
freely and more deeply than early potatoes." In this instance he found that 
the roots reached a depth of 3 feet and that the lateral roots were interlaced 
between the hills, which were 3 feet apart. He stated that the roots were 
very tender and were badly broken by washing. In 1900 he again investi- 
gated the roots of Early Ohio potatoes at Fargo and found that 43 days after 
planting they lay for the most part within the first 8 inches of soil. A few 
penetrated to a depth of 1.5 feet and some of the horizontal ones reached a 
length of 2 feet. Few fibrous roots were found. At maturity the roots had 
penetrated to a depth of 2.5 feet. Rotmistrov (1909), working at Odessa, 
Russia, stated that the potato, unlike most dicotyledons, has many main 
roots, and again at the same station (1914) concluded that the root systems 
of potatoes are very short, being approximately 2 feet. 



30 



Development and Activities of Roots of Crop Plants. 



A comparison of these results with those obtained at Peru shows a much 
more extensive root development at the latter station. At the New York 
Experiment Station only was the lateral spread as great, while in no case 
was the depth of penetration so pronounced. These differences may be due 
in part to the variety of potato grown, and to variations in environmental 
conditions both climatic and edaphic. It seems, however, that, at least m 
some cases, the method of excavation was faulty, in that the entire root 
system was not recovered. In most cases the roots were washed out, and 
the fragile younger and finer parts largely destroyed. In some instances, 
too, it seems clear that the block of earth prepared for washing was not 
extensive enough to include all of the roots. 

Comparison of Root Systems. 
The most obvious conclusion from a consideration of the data is that these 
crop plants, like the prairie species that preceded them, are provided with 
well-developed, deep-seated, and extensive root system (c/. Weaver, 1919, 
1920). All of the cereal crops examined are similar in having two more or 
less distinct parts of the root system as regards position. One group of 
roots in each case spread out horizontally in all directions from the base of 
the plant and had for its main function absorption from the shallower stratum 
of soil. In most instances these lay within a foot of the soil surface. The 
other group of roots, which completed the underground part of each plant, 
pursued a more or less vertically downward course and penetrated deeply. 
The potato also had a shallower and a deeper portion of its root system. How- 
ever, in the development of the potato this end is accomplished in a different 
manner. Instead of having two more or less different groups of roots, as 
in the cereals, the same group served both purposes. This was brought about 
by developing at first a copiously branched, shallow, horizontal group of 
roots Later, by turning rather abruptly downward and continuing their 
course into the subsoil, these also became the deeply penetrating ones. In time 
of development of these two portions of the absorbing system, the plants 
fall naturally into two groups; the small cereals forming one group, and corn 
and potatoes comprising the other. In the former group both the shallow 
and the deeper penetrating portions began to form more or less simultaneously 
in the earlier stages of growth. In the latter the shallow system had devel- 
oped to a rather marked degree before the deeper penetration of the soil 
began. However, both groups agreed fairly well in that the shallow roots 
had practically reached the limit of their horizontal spread by the tune the 
tops were in the intermediate stages of growth. Conversely, the longer 
roots continued to penetrate deeper until the plants were almost if not indeed 
entirely mature. . , . ■; ; , , 

All the root systems, as might be expected considering their fibrous char- 
acter were well supplied with small branches. But in this particular an 
examination of the figures shows that the corn and potato were much more 
abundantly furnished with branches than were any of the others. A com- 
parison of the relative development of tops and roots shows the greater 
extent of the underground parts in every case except that of corn, lhey 
regularly penetrated to a depth at least twice as great as the height of the 
tops Indeed, in some instances, especially among the smaller cereals, the 



Investigations at Peru, Nebraska. 



31 



root extent was even much greater. In regard to corn, height growth and 
root depth were about equal. However, what the corn lacked in relative 
depth was adequately compensated for by widely penetrating and exceed- 
ingly well branched roots. A comparison of the seedling stages of wheat and 
oats shows that the roots of the former spread more widely. At this stage 
of development the wheat roots were lighter in color, tougher, and, although 
abundantly supplied with root-hairs, they did not occur in such density as 
on the oats. The surface roots of wheat, when compared with those of 
oats and barley, are found to be both less numerous and extensive. Thus, 
the ability of oats to more thoroughly exhaust the surface soil of water and 
nutrients, a belief current among agriculturalists, may have some foundation 
in fact. Root habit gives a clue to the cause of this phenomenon. 

Table 1 gives a summary of the development of the several crops at various 
stages of growth and affords an easy basis for comparison. 



Table 1. — Development of crops at Peru, Nebraska, 1919. 



Crop. 


Age 
of 
plants. 


Aver- 
age 

height. 


Stage of 
development. 


Maxi- 
mum 
depth. 


Maximum 
lateral 
Bpread. 


Remarks. 




days. 


feet. 




feet. 


feet. 




Oats, University No. 21 . 


18 


0.2 


1 leaf 


0.7 


0.4 


3 or 4 roots. 


59 


1.1 




3.6 


1.0 


1 or 2 tillers. 




92 


3.0 




6.7 


1.4 


1 or 2 tillers headed. 


Oats, Swedish Select. . . . 


19 


0.2 


1 leaf 


0.8 


0.4 


3 or 4 roots. 




60 


1.0 




3.7 


0.8 


1 to 3 tillers. 




93 


3.0 




6.8 


1.3 


1 or 2 tillers headed. 




19 


0.3 


1 leaf 


0.7 


0.4 


4 or 5 roots. 




60 


0.8 


5 leaves 


4.5 


1.3 


1 to 3 tillers. 




95 


2.5 


Stiff -dough stage 


7.4 


1.2 


1 tiller headed. 


Wheat, Marquis 


20 


0.2 


Second leaf unfolding. 


0.9 


0.6 


3 to 5 roots. 




70 


1.7 


5 leaves, jointing 


5.8 


1.3 


1 to 3 tillers. 




93 


2.7 


Stiff -dough stage 


6.7 


1.3 


1 tiller headed. 


Barley, Manchuria 


20 


0.4 


Second leaf unfolding. 


1.2 


0.7 


5 to 7 roots. 


54 


0.9 




4.5 


1.3 


1 to 3 tillers. 




84 


2.3 




6.3 


1.3 


1 or 2 tillers headed. 


Corn, Iowa Silver Mine. 


36 


1.0 


7 or 8 leaves 


1.3 


2.6 


12 to 15 roots. 




57 


4.0 




4.7 


4.0 


Plants growing vigor- 














ously. 




116 


8.5 




8.2 


4.0 


Greater part of leaves 














green. 


Potatoes, Early Ohio. . . 


56 


0.9 


Tubers appearing 


1.5 


2.2 


As many as 55 roots. 


94 


2.3 


One-third leaves dead. 


4.7 


2.1 


Roots variable in num- 














ber and extent. 



Some preliminary examinations were made of the development of roots 
and above-ground parts of crop plants when grown as isolated individuals. 
In general, both were found, in every case, to be more extensive than where 
the crops were grown under the competition of normal field conditions (cf. 
Weaver, 1920). 



32 Development and. Activities of Roots of Crop Plants. 

Environmental Conditions of Growth. 

To understand the causes of such remarkable root development, it will 
be necessary to consider somewhat in detail the environmental conditions 
under which the crops grew. 

The mellow silt-loam soil, underlaid at a depth of 1 to 1.5 feet with loess 
of very loose texture, not only absorbs water readily, but has a high water- 
holding capacity. This ranges from 57 to 64 per cent and is rather uniform 
to a depth of at least 4 feet, the same type of subsoil extending to depths of 
many feet. The mechanical analyses of these soils (table 2) shows that they 
are approximately one-half silt, while the remainder is almost entirely com- 
posed of very fine sand and clay. 



Table 2. — Mechanical analyses of soils from Peru. 



Depth of 
sample. 


Coarse 
gravel. 


Fine 
gravel. 


Coarse 
sand. 


Medium 
sand. 


Fine 
sand. 


Very fine 
sand. 


Silt. 


Clay. 


Hygroscopic 
coefficient. 


feet. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


0.0 to 0.5 


0.0 


0.0 


0.0 


0.3 


1.8 


32.0 


46.2 


19.7 


8.9 


0.5 to 1.0 


0.0 


0.0 


0.4 


0.7 


1.0 


27.9 


50.6 


19.4 


9.1 


1 to 2 


0.0 


0.0 


0.1 


0.2 


1.8 


27.7 


50.1 


20.1 


8.9 


2 to 3 


0.0 


0.0 


0.1 


0.4 


1.8 


26.9 


54.6 


16.2 


8.8 


3 to 4 





0.0 


0.0 


0.1 


0.4 


33.5 


55.3 


10.7 


9.2 



The chemical analyses are given in table 3. According to the Truog test, 
the soils were slightly acid. The volatile matter and nitrogen are not low, 
while the other critical elements are present in sufficient quantities to assure 
good yields. 

Table 3. — Chemical analyses of soils from Peru. 1 



Depth of sample. 


Acidity. 


Volatile 
matter. 


Phosphorus 
pentoxide. 


Sulphur 
trioxide. 


Potassium 
oxide. 


Nitrogen. 


feet. 




p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


0.0 to 0.5 


Slight 


4.72 


0.308 


0.006 


1.91 


0.178 


0.5 to 1.0 


Do. 


4.59 


0.308 


0.005 


2.02 


0.164 


1 to 2 


Do. 


4.88 


0.267 


0.004 


2.21 


0.139 


2 to 3 


Do. 


3.59 


0.296 


0.003 


1.93 


0.084 


3 to 4 


Very slight. 


2.77 


0.173 


0.015 


1.98 


0.048 



i Phosphorus determinations were made by digestion with HNO3 and HF; sulphur by fusion 
with NaaOa; potassium by fusion with calcium carbonate; and nitrogen by the modified Gunning 
method. 



As pointed out elsewhere, (Weaver, 1920 : 100) the chief limiting factor to 
crop production in the grassland area west of the Missouri is soil-moisture. 
In general, it may be stated that in eastern Nebraska most of the precipitation 
falls during the growing-season and less than one-tenth of it during the three 
winter months. About half of the rainfall of May, June, and July is from 
rains of an inch or more in 24 hours. Such a seasonal distribution of moisture 
is very favorable for the growth of crops. Not infrequently, however, storms 
occur with a rainfall exceeding 2 inches and occasionally 4 or 5 inches in a 
period of 24 hours. Such storms invariably result in a high run-off, and they 



Investigations at Peru, Nebraska. 



33 



account largely for the observed deficiencies of moisture for crops in seasons 
where the recorded rainfall would indicate an abundant supply. The mean 
annual precipitation at Peru is about 34 inches. In table 4 is given the 
monthly precipitation from March to August 1919, together with the mean 
for the five preceding years. 



Table 4. — Precipitation in inches. 



Year. 


March. 


April. 


May. 


June. 


July. 


August. 


Total. 


Mean, 1915 to 1919 


1.2 


2.7 


5.4 


4.6 


3.2 


3.1 


20.2 


1919 


2.0 


4.6 


1.8 


4.3 


0.8 


1.6 


15.1 



These data were obtained from the reports of the U. S. Weather Bureau 
station at Nebraska City, Nebraska, 15 miles north of Peru. March and 
June were months of rather normal rainfall; April was unusually wet, while 
May, July, and August had a precipitation far below the average. The only 
deviation of any importance from these Nebraska City records was July 4 
and 5, when two very heavy local showers occurred at Peru. About 2 inches 
of water fell during a period of 2 hours or less. This resulted in a high run- 
off. Nevertheless, these showers were very beneficial to the growing crops. 
However, precipitation is only a very general indicator of conditions for plant 
growth. Because of differences in time and manner of distribution, amount 
of run-off, which in turn is influenced by soil structure, rapidity of evaporation, 
etc., rainfall alone, indeed, yields data of little value in a study of the water 
relations for crop production. Although it modifies the temperature of both 
air and soil, and especially the humidity, as well as having a profound effect 
upon soil aeration, its major influence upon the activities of plants is exerted 
through its power to replenish soil moisture. The soil may be compared 
to a great reservoir of water from which growing plants are constantly draw- 
ing their supply. When water becomes less abundant in the upper portion 
of this reservoir, plants must either suffer from lack of water or extend their 
absorbing organs into the deeper soils. Hence it may be that during this 
season of drought the roots penetrated somewhat deeper than normally. 
However, similar results were obtained at this station during 1921, but this 
was also a year of deficient rainfall. Further studies may show this root 
habit is quite normal for these rather mellow and relatively well-aerated 
soils of loose texture, where the subsoil is moist to very great depths. In 
fact, judging from the root habits of native species, this seems highly probable. 

Water-content of the soil, with its effect upon aeration, is the most im- 
portant factor affecting root development under field conditions. Because 
of its importance, a rather extensive series of determinations was made. 
In taking the samples of 100 to 150 grams of soil at various depths, a Briggs 
geotome was employed. The soil was dried to a constant weight at 105° C. 
and the water-content calculated in per cent of the dry weight. For con- 
venience, the water in excess of the hygroscopic coefficient is considered avail- 
able for plant growth. In another place (Weaver, 1920 : 28), it has been 
pointed out that soil upon which native prairie or short-grasses grow fre- 
quently shows a water-content below the wilting coefficient of Briggs and 



34 



Development and Activities of Roots of Crop Plants. 



Shantz (1912), at least to a depth of 4 or 5 feet. On the other hand, during 
7 years of field work in many States, the senior writer has never found the 
water-content to fall below the hygroscopic coefficient, except in the surface 
soil, where direct evaporation rather than absorption by plants was the cause. 
These findings are quite in agreement with those of Alway and others (1919). 
However, it should be made clear that we are not at all certain that crop 
plants are as efficient in exhausting the water-supply as is native vegetation. 
Moreover, it may be found that certain plants of either group are more or 
less efficient than others. The thorough distribution of a minutely branched 
root system through all parts of the soil, as already described, would promote 
efficient absorption. 

In figure 12 the available water-content of the soil is given to a depth of 
3 feet from March 31 to June 16. A glance at this figure shows clearly the 




o ' i i — * 

Fio. 13. — Water-content in excess of hygroscopic coefficient 
in the several crop plats on May 30. 

rather uniform distribution of moisture, as well as the fact that practically 
throughout the entire period a minimum of 14 per cent was available at 
all levels. Since the hygroscopic coefficients of these soils vary from 8.9 
per cent (surface 6 inches) to 9.2 per cent (fourth foot), the actual water-content 
for the period did not fall below 21 per cent. These data are from an open 
space 10 feet square in the corn plat. Water losses here were by surface 
evaporation only. Later in the season the area was occupied in part at least 
by the widely extending roots of the corn, and further water-content deter- 
minations were not made. 

The water available to the various crops at the several levels on May 30 
is given in figure 13. At this time no marked differences in the water-content 



Investigations at Peru, Nebraska. 



35 



of the several plats are apparent, except that the oat plats were drier in the 
surface 6 inches, and those of corn showed more available water at all levels 
to 3 feet than the cereals which were planted earlier. At this time the latter 
were about 12 inches tall, and, although the main development of roots was 
in the surface 2 feet of soil, not a few extended into the third foot or beyond 
(cf. figs. 1 a, b and 3 b, c). The younger corn plants had rooted much 
more superficially, and the total transpiring surface was less extensive than 
in the smaller cereals at this time. However, from the uniformity of the 
water-content in the third foot, it seems clear that little absorption had 
occurred at this level. The water relations of the soils in the several plats 
on June 23 are shown in figure 14. The small percentage of available water 
at all levels, when compared with conditions on May 30, is at once evident, 
and shows clearly that the roots were probably extracting water at depths 
of at least 3 feet. 

It is interesting to compare the water-content of the oat plats with that 
of wheat and barley. On June 23 the average water-content of the two 
oat plats was only 70 per cent of the average of the two wheat plats, and 65 
per cent of that of the barley plat. Five days later, on June 28, the average 
water-content of the oat plats was 76 per cent of the average of the wheat 
plats and 77 per cent of that of the barley plat. In other words, on June 
23 the oat plats contained 30 per cent less moisture than the wheat plats and 
35 per cent less than the barley. On June 28, the oat plats contained 24 
per cent less moisture than the wheat and 23 per cent less than the barley. 
This agrees well with the root habit. A comparison of the mature root sys- 
tems (figs. 2, 4, and 6) shows at once that the number of deeply penetrating 
roots of oats is 1 or 2 greater per plant than that of wheat and 3 or 4 greater 
than that of barley. It is also possible that oat roots are more efficient 
absorbers than those of wheat and barley. 



OATS OATS BARLEY WHEAT WHEAT CORN 



























J'-z' 












**** " 







Fig. 14. — Water-content in excess of hygroscopic coefficient 
in the several plats on June 23. 

The relative available water-contents of the potato and corn plats are also 
significant. On June 28, at practically every level represented, the potatoes 
had exhausted the soil-moisture more completely than had the corn (table 5). 
The average of all depths gave 10 per cent less in the potato plat. But 9 
days later, on July 7, the corn, responding to the ideal growing weather by 
a very rapid development of the top, had reversed these conditions, for 
the corn plat now had approximately 10 per cent less moisture than the potato 
plat. A week later, July 15, this difference had increased to 19 per cent. 
Another factor occurring during this two-week period may have had some 



36 Development and Activities of Roots of Crop Plants. 

influence on the water-content relations. The potato leaves had begun to 
wither and die. However, it seems probable that the rapid development of 
the aerial parts of the corn was the major cause of decreased water-content. 



Table 5. — Water-content in excess of hygroscopic coefficient in the corn 
and potato plats. 





June 28. 


July 7. 


July 15. 


Depth 


























in feet. 














Potato. 


Corn. 


Potato. 


Corn. 


Potato. 


Corn. 


0,0 to 0.5 


10.3 


10.4 


14.7 


14.0 


9.4 


7.3 


0.5 to 1 


8.5 


11.9 


17.9 


15.6 


14.2 


10.1 


1 to 2 


11.7 


11.3 


15.4 


13.3 


13.0 


11.5 


2 to 3 


10.8 


12.2 


13.4 


12.8 


13.1 


11.5 


3 to 4 


11.9 


12.1 










4 to 5 


11.1 


13.6 











An examination of table 6 shows how efficient is the massive, deeply pene- 
trating root system of corn. During the dry month of August the available 
moisture had been reduced to only 4 or 5 per cent, even to a depth of 5 feet. 



Table 6. — Water-content in excess of the hygroscopic coefficient in the corn plat. 



Depth in feet. 


July 22. 


July 29. 


Aug. 5. 


Aug. 12. 


Aug. 20. 


Aug. 25. 


Sept. 2. 


0.0 to 0.5 


2.7 


0.1 


20.8 


2.0 


1.5 


4.0 


1.5 


0.5 to 1 


5.5 


2.6 


2.9 


7.9 


5.4 


4.9 


4.3 


1 to 2 


8.4 


7.2 


4.4 


8.5 


6.1 


4.9 


5.1 


2 to 3 


10.9 


6.1 


4.2 


8.2 


5.6 


6.0 


3.9 


3 to 4 




11.1 










2.9 


4 to 5 




13.1 










3.4 



The enormous transpiring surface presented by a field of corn should be 
emphasized. Kiesselbach (1916) has calculated that an acre of corn in east- 
ern Nebraska planted in hills 3.5 feet apart with 3 plants per hill has a tran- 
spiring surface of approximately 4 acres. Closely correlated with the devel- 
opment of the transpiring area is the growth of the absorbing system. Fig- 
ures 8 and 9 well illustrate the enormous absorbing area of a single stalk, 
while table 6 indicates the degree to which this cereal exhausts the available 
moisture even to a depth of 5 feet. 

Soil temperature is an important ecological factor affecting root growth. 
Like soil aeration, it affects the development of the root system not only 
directly, but also plays a part in the life activities of soil micro-organisms. 
These may affect the plants directly or alter the chemical composition of the 
soil and thus influence the root environment, which in turn may modify 
its development. The importance of temperature in the development of 
root systems has only recently been emphasized (Cannon, 1918), and com- 
paratively few investigations have been made on the evaluation of this 
factor in root growth. An examination of figure 15, which gives thermometer 
readings at various depths, shows at once that the temperature of the wet 



Investigations at Peru, Nebraska. 



37 



soil was quite too low for maximum root development during the cold rainy 
month of April (cf. Lehenbauer, 1914). During May, a slow but uniform 
rise occurred, while differences between the temperatures on June 9 and 23 
were quite pronounced. This ushered in a hot, dry period which extended 
to July 4. It is interesting to note that the deeper soils into which the new 
roots were extending were progressively colder. Undoubtedly temperature 
has a marked influence upon crop-root development under field conditions. 



April 

14 



May 

12 20 



June 









































/ / 


















3" 


















/ / 
/ / 


3' 


r s 






'//'/ 


% 



































Fig. 15. — Soil-temperatures at various depths during 1919. 



May June 

5 12 19 26 2 9 16 23 



July 



August 



15 22 29 7 12 20 25 




Fig. 16. — Average day and night temperatures (solid lines) 
and average maximum and minimum temperatures. 

Indeed, it has been suggested (Shepperd, 1905) that in northern latitudes, 
where the ground freezes deep in the winter, the soil may be too cold for the 
roots of cereals to penetrate to a depth greater than 3 feet before midsummer 
(cf. Pulling, 1918). 

The average weekly day and night temperatures are shown in figure 16, 
which also includes the average weekly maximum and minimum tempera- 
tures. The average for the day temperatures was determined from the 



38 



Development and Activities of Roots of Crop Plants. 



weekly record-sheets of the thermographs by adding the temperatures begin- 
ning at 8 a. m. and every 2 hours thereafter until 6 p. m. for each day and 
dividing the sum by the total number of 2-hour intervals. Those for the 
night intervals were calculated in a similar manner, beginning at 8 p. m. and 
including the readings until 6 a. m. The weekly maximum and minimum 
readings were determined directly by averaging the 7 highest and 7 lowest 
points respectively, on the weekly record-sheet. This method of evaluating 
temperatures takes into account both temperature extremes and the element 
of time. A gradual increase in temperature with the progress of the season 
is evident. The high temperatures during July and August were very 
favorable for the rapid development of corn. 

The factors of high temperature, low humidity, and wind movement com- 
bine to increase the evaporating power of the air and transpiration of crops. 
In a study of root development it is important to consider the above-ground 
environment. For just as the possible growth of the aerial parts of plants 
is affected by the extent of the development of the root system, conversely 
the environmental conditions to which the aerial parts are subjected, espe- 
cially as concerns their water relations, must reflect themselves in root devel- 
opment. Table 7 shows the average daily evaporation losses during the 

Table 7. — Average daily evaporation at Peru, 1919. 



Apr. 21 to 28 5.8 

Apr. 28 to May 7 11.8 

May 7 to 12 20.0 

May 12 to 20 24.0 

May 20 to 28 28.3 

May 28 to June 9 19.0 

June 9 to 16 21.4 



c.c. 

June 16 to 23 27.3 

June 23 to 30 26.6 

June 30 to July 8 20.9 

July 8 to 15 27.0 

July 15 to 22 22.7 

July 22 to 29 44.1 

July 29 to Aug. 5 38.4 



several periods from April 21 to August 5. An examination of these data 
reveals no unusually high evaporation rates when compared with other 
seasons 1 (Weaver 1919, 1920), except during the latter part of July and early 
in August. At this time all of the crops except corn were ripe. During the 
remainder of August only one or two light showers occurred and the tempera- 
ture most of the time was quite high (fig. 16). These conditions doubtless 
reflected themselves in the extensive root development of the corn. 

Summary of Root Development. 

All the cereals, including corn, possessed a root system' in which there was 
a definite group of more or less horizontal, spreading roots lying within the 
first 1 to 1.3 feet of soil, and a second group of deeply penetrating roots ex- 
tending into the subsoil to depths of 6 or 7 feet. 

The Early Ohio potato differed from the other plants in that the same group 
of roots which at the outset formed the shallow portion of the system subse- 
quently became the deeper portion by turning more or less abruptly to the 
vertical position and growing downward. 

In every instance the root systems were very extensive in relation to the 
size of the top. All the main roots were abundantly supplied with branches 

1 Since these atmometers were not fitted with non-absorbing apparatus, direct comparisons 
of actual losses can not be made but it is certain losses were higher than the figures indicate. 



Investigations at Lincoln, Nebraska. 



39 



that greatly increased their absorbing area. This was especially marked 
in the case of corn and potatoes. 

The more superficial roots reached their maximum development first. In 
most cases this occurred about the time the top had reached an intermediate 
stage of growth; the deeper roots developed coordinately with the top and 
thus balanced water absorption and transpiration. 

Oats reduced the soil moisture to a greater degree than any of the other 
small cereals. Corn in its later stages of growth was an extravagant user of 
water. The potato showed the greatest variation in the number and extent 
of its roots. 

The root systems of isolated crop plants are greatly modified as to nature 
and extent when compared with similar plants grown under the competi- 
tive conditions imposed by the rate of planting in ordinary field practice. 

The season in which this investigation was carried on had a deficit of rain- 
fall, particularly during the months of May, July, and August. The defi- 
ciency was sufficient to mark it as a dry crop-year. 



40 



Development and Activities of Roots of Crop Plants. 



II. INVESTIGATIONS AT LINCOLN, NEBRASKA, IN 

1919 AND 1920. 

The root development of crop plants at Lincoln has been studied for the 
seasons of 1919 and 1920. Data on the root relations of 4 leguminous crops, 
4 forage plants, sunflowers, and oats, in both upland and lowland areas, dur- 
ing 1919, have already been published (Weaver, 1920). During 1920, root 
studies were continued, with particular reference to the successive stages 
in the development of oats, wheat, barley, alfalfa, and sweet clover and their 
correlation with environmental factors. In these experiments White Kherson 
oats, Marquis Spring wheat, and Manchuria barley were grown. The seed 
of these and also of alfalfa and white sweet clover were obtained from a 
local seed company. 

The cropped areas were the same as those used the preceding year. The 
upland plats were located about 3 miles north of Lincoln, on a broad, level 
hilltop. The soil is a silt-loam of fine texture, but much more compact than 
that at Peru. The lowland station was located about a mile south of the 
former and on the edge of the flood-plain of Salt Creek, in rich alluvial silt- 
loam. 

Mechanical analyses of the soils are given in table 8, together with the 
moisture equivalents computed from the mechanical composition by the 
formula of Alway and Russel (1916 : 842). These data show that both 
soils are fine-textured, being composed mostly of silt and clay. A study of 
the table shows that they are remarkably similar. 



Table 8. — Mechanical analyses of soils from Lincoln. 



Depth of sample. 


Coarse 
gravel. 


Fine 
gravel. 


Coarse 
sand. 


Medi- 
um 
sand. 


Fine 
sand. 


Very- 
fine 
sand. 


Silt. 


Clay. 


Moisture 
equiva- 
lent. 


Upland plats: 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


0.0 to 0.5 foot 


0.0 


0.0 


0.3 


0.5 


1.6 


19.8 


48.6 


29.2 


31.4 


0.5 to 1.0 foot 


.0 


.0 


.2 


.6 


1.3 


16.7 


52.4 


28.8 


31.8 


1 to 2 feet 


.0 


.0 


.1 


.2 


0.8 


16.7 


55.6 


26.6 


31.5 


2 to 3 feet 


.0 


.0 


.1 


.1 


0.5 


19.0 


57.9 


22.3 


30.1 


Lowland plats: 




















0.0 to 0.5 foot 


.1 


.4 


2.2 


1.8 


5.0 


25.0 


41.3 


24.3 


27.7 


0.5 to 1.0 foot 


.3 


.7 


2.1 


2.2 


5.0 


25.4 


38.8 


25.8 


27.9 


1 to 2 feet 


.2 


.3 


1.3 


1.5 


3.7 


21.4 


40.8 


31.0 


30.6 


2 to 3 feet 


.0 


.1 


0.4 


0.5 


1.7 


19.2 


43.4 


34.7 


32.9 



Table 9 gives the chemical composition of representative composite sam- 
ples of soil at various depths from the two areas. A study of the table shows 
that the soils at the two stations are not strikingly different. It may be 
noted that the lime-content is about the same in both fields. However, the 
greater amount of volatile matter and the greater nitrogen-content at all 
depths indicate more favorable conditions for growth in the lowland plats, 
and this probably accounts in part for the more rapid growth and better 
development of the crops in this field. The soil in both fields showed medium 
acidity in the first foot, slight in the second, very slight in the third, while 
the fourth foot showed no acidity, but was slightly carbonaceous. 



Investigations at Lincoln, Nebraska. 



41 



Both areas had been cropped for many years. The crop of the preceding 
year in the upland was Sudan grass; the lowland area had lain fallow. The 
cereals were sown in alternating strips, 100 feet long and 10 feet wide, with 
planted discard areas between. On the upland the plats were all in dupli- 
cate. The rate of seeding for oats, wheat, and barley was 56, 75, and 60 
pounds per acre, respectively. Alfalfa and sweet clover were seeded at the 
rate of 12 pounds per acre in plats 50 feet long and 10 feet wide. 



Table 9. — Chemical analyses of soils by digestion with hydrochloric acid (sp. gr. 1.115) for 

120 hours. 



Depth of sample. 


Insolu- 
ble 
resi- 
due. 


Solu- 
ble 
salts. 


Vola- 
tile 

mat- 
ter. 


Iron 
and 

alumin- 
ium 

oxides. 


Cal- 
cium 
oxide. 


Mag- 
nesium 
oxide. 


Phos- 
phorus 
pent- 
oxide. 


Nitro- 
gen. 


Upland plats: 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


0.0 to 0.5 foot 


76.87 


17.12 


6.01 


13.20 


0.68 


1.19 


0.13 


0.159 


0.5 to 1.0 foot 


75.70 


18.58 


5.72 


14.25 


.70 


1.32 


.12 


.134 


1.0 to 2.0 feet 


76.17 


19.08 


4.75 


14.72 


.75 


1.68 


.12 


.079 


2.0 to 3.0 feet 


77.86 


18.46 


3.68 


14.03 


.86 


1.69 


.15 


.045 


Lowland plats: 


















0.0 to 0.5 foot 


79.34 


12.96 


7.70 


9.57 


.68 


.75 


.13 


.218 




79.63 


13.66 


6.71 


10.27 


.63 


.77 


.10 


.187 




78.11 


15.83 


6.06 


12.11 


.64 


1.01 


.08 


.135 


2.0 to 3.0 feet 


74.78 


19.82 


5.40 


15.20 


.76 


1.27 


.09 


.082 



Preparatory to seeding, both fields were plowed to a depth of 5 inches on 
March 29 and repeatedly harrowed until a good seed-bed was formed. All 
of the crops on the upland were planted on March 31, while the lowland 
area, because of winter weather, was not seeded until April 9. At the time 
of planting both fields were in excellent tilth. The seed was sowed broad- 
cast by hand and hoed in to a depth of 1 to 3 inches. To assure uniform seed 
distribution, each plat was subdivided into areas only 10 by 25 feet, and the 
appropriate amount of seed scattered very evenly over each area. After 
planting, no further attention was given to the cultivation of the crops, except 
to pull out the larger weeds from the grain fields and keep the plats of legumes 
clean in a similar manner. 

Oats, Avena sativa. 

The first examination of root development was made on May 1, in the 
upland plats, 31 days after planting. The crop was evenly developed, with 
an average height of 2 inches and a maximum leaf -length of 3 inches. About 
half of the plants had only one leaf unfolded; on the rest the second leaf varied 
from a few millimeters to over 2 inches in length. Some of the plants had 
only 3 roots, but most of them had 5 to 7. The primary roots, or at least 
one of them, reached a maximum depth of 7 or 8 inches; the younger roots 
were only 1 to 4 inches in length. The working depth of the roots was about 
5 inches. Where the seed had been planted more than 1.5 inches deep, a 
pair of unbranched roots about 0.3 inch in length had arisen from opposite 
sides of the node about an inch below the soil surface. On all of the other 



42 



Development and Activities of Roots of Crop Plants. 



roots, laterals from 0.1 to 1 inch in length occurred at the rate of 7 to 15 per 
inch, except near the root-ends, 0.5 to 2 inches of which were unbranched. 
All of these laterals were of the first order only (fig. 17). The primary set 
of roots spread laterally at an angle of about 45 degrees from the vertical; 
the maximum lateral spread on any side of the plant did not exceed Slnches! 

The slow rate of development was due to adverse growth conditions. In 
fact, during this period of 31 days, the growth was about equal to that of 
18 days at Peru (cf. p. 31). Rotmistrov (1909 : 33) found the roots of oats, 
wheat, and barley had an average depth of 12 inches only 7 days after the 
appearance of the sprout. He does not record the environmental conditions 
of the plants. In our experiment the influence of temperature is clearly 
shown by the fact that oats planted in the same field on May 15 revealed a 
much more advanced development of both shoot and root 15 days later than 
had occurred in a month when the seed was sowed on March 31. Thus, the 
very slow development of oats is clearly correlated with the unfavorable 
conditions for growth. Throughout the month of April the weather was 
cold and wet. Excessive cloudiness prevailed and there was a large defi- 
ciency m sunshine. The ground was frozen for several days following April 
2, and more or less covered with snow from April 2 to 9, while freezing tem- 
peratures with light snow occurred during the latter half of the month. 



There were only 6 clear days. The soil was wet and cold. A water-content 
of about 22 per cent was rather evenly distributed throughout the first 5 
feet of soil. Thermograph records from a depth of 6 inches in an adjoining 
prairie, 1 gave an average temperature of about 47° F. for the last 15 days 
of April. During this period the minimum soil temperature fell to 42° F., 
and at no time did the maximum exceed 54° F. On May 5 the soil tempera- 
ture at depths of 0.5 to 2 feet in the crop plats ranged from 61° to 54° F. 
respectively. 

1 Thermographs and evaporimeters were installed in native grassland areas adjoining the crop 
plats at all the stations except Peru, in connection with "Transplant Quadrats and Areas" (see 
Year Book, Carnegie Institution of Washington, 1920 : 355) 




A 



B 



Fig. 17.— A and B. Oats 31 days old. 



Investigations at Lincoln, Nebraska. 



43 



On May 15, when the plants were 45 days old, a second examination was 
made. They had an average height of about 4 inches and on most of them 
the fourth leaf was fairly well developed. They had not yet begun to tiller. 
The number of roots varied from 7 to 14, with an average of about 8. The 
longer ones penetrated to depths of 1.6 to 2 feet, while the maximum lateral 
spread did not exceed 0.5 foot. Some of the younger roots were only 1 to 4 
inches long and without branches. They extended in a horizontal or oblique 
direction, the longer ones sometimes being fairly well supplied with short 
laterals of the first order. On the older roots, branches of the second order, 
some nearly an inch in length, occurred, but they were not abundant. The 



primary laterals, especially in the surface 8 inches of soil, had reached a 
length of 1 to 3 inches. Below 8 inches depth, only laterals of the first order 
were found, and none exceeded 0.8 inch in length, while frequently the last 
6 or 8 inches of the glistening white roots were entirely destitute of branches. 
On seeds that were planted deep, a whorl of 4 to 6 roots had developed an 
inch below the surface (fig. 18). The root system had a working depth of 
about 7 or 8 inches. Thus, during this interval of 15 days, although growth 
conditions were more favorable than before, the plants continued to develop 
slowly. 




A 



8 



Fia. 18. — A and B. Oats 45 days old. 



44 



Development and Activities of Roots of Crop Plants. 



The weather for the most part remained cold and cloudy, but no frost oc- 
curred. The water-content of the soil averaged about 30 per cent. The soil 
temperatures remained low (minimum 52°, maximum 66° F., at a depth of 
6 inches). Air temperatures, recorded by a hygrothermograph, appropriately 
sheltered and placed with the recording appa- 
ratus 4 inches above the soil surface in an 
adjacent prairie, gave an average day reading 
of about 63° F., while the average night tem- 
perature was only 53° F. The relative humidity 
was high. 

Rotmistrov (1909 : 34) states that at the end 
of 21 days after the appearance of the sprout, 
not only was the extreme breadth of the root 
system marked off, but the depth of penetra- 
tion reached 0.5 meter and roots of the third 
order were clearly visible, the whole 
forming a felt-like entanglement. 
Clearly our plants were developing 
more slowly. However, oats planted 
May 4, and examined 26 days later, 
were further developed than 45-day- 
old plants just described. They were 
5 inches high, had 5 leaves each, and 
some had tillers. The root growth 
was proportional. It is interesting 
to note also the more rapid root 
penetration of White Kherson oats 
in the loess soils at Peru. Here 
plants only 14 days older than those 
just described had extended their 
roots into the fourth foot of soil. 

Fifteen days later, on May 30, the 
root development was again studied. 
During this period both roots and 
shoots had grown rapidly. Although 
the soil remained quite wet (25 to 30 
per cent water-content), it was con- 
siderably warmer, the average daily 
temperature during the last week of 
May reaching 71° F. at a depth of 6 
inches. This was higher than the 
average air-temperature (65° F.) for 
the same interval. Fewer rains and 
less cloudy weather occurred during 
this last half of the month, although 
the humidity remained high. 

The average height of the plants was about 9 inches, but some were 3 inches 
taller. Each plant had 7 to 9 leaves, one or two of the oldest ones being 
either dead or rapidly deteriorating. About one-tenth of the plants had 




Oata 60 days old. 



Investigations at Lincoln, Nebraska. 



45 



developed one or two tillers. Root counts of a large number of individuals 
gave a total of 16 to 27 per plant. Several roots were traced to a maximum 
depth of 2.7 feet, the average maximum depth being about 2.3 feet. The 
average lateral spread was only 6 inches, although some roots extended hori- 
zontally or obliquely away from the plant to a distance of 7 or 8 inches. 
The working depth had reached the 1.5-foot level. Besides the greater num- 
ber of primary roots, their wider spread, and deeper penetration, there was a 
greater development of laterals, both in number, length, and secondary 
branching. Many of the younger roots near the soil surface spread laterally 
only 3 or 4 inches; in general, the widest-spreading roots ended in the surface 
4 to 8 inches of soil. In the first 8 to 12 inches of soil the abundant laterals 
sometimes reached a length of 0.2 to 2.5 inches; secondary branches were few 
and seldom more than 0.3 inch long. At greater depths the branching was 
much poorer and the laterals shorter, in fact, the last 6 to 12 inches of the 
thick, straight, white root-ends were devoid of branches (fig. 19). 

The fourth examination was made on June 19 and 21, when the plants, 
now 80 days old, were beginning to blossom. They had an average height 
of about 2 feet, although some were 4 inches taller. Many of the plants had 
only 1 stem, others had from 1 to 5 tillers each, while perhaps 2 was an 
average. 



Table 10. — Water-content in excess oj hygroscopic coefficient in the crop plats at Lincoln, 1920. 



Date. 


to 0.5 foot deep. 


0.5 to 1 foot deep. 


1 to 2 feet deep. 


2 to 3 feet deep. 


3 to 4 feet deep. 
























Upper. 


Lower. 


Upper. 


Lower. 


Upper. 


Lower. 


Upper. 


Lower. 


Upper. 


Lower. 


Mar. 31 


13.0 




16.1 




15.2 




14.1 




11,3 




Apr. 10 


18.8 


18.7 


18.1 


19.4 


16.0 


17.0 


16.1 


15.1 


14.6 


14.1 


May 4 


20.9 








22.1 












May 15 


20.7 


20.5 


19.2 


21.5 


23.9 


24.8 










June 3 


16.6 




18.8 




16.5 




15.5 








June 4 




il.i 




19.0 




17.5 




15.0 




17.1 




5.3 


13.0 


8.3 


16.1 


12.5 


7.6 


15.4 


12.1 


16.6 


15.9 


June 24 


1.3 


1.7 


8.5 


9.7 


9.7 


10.1 










July 14 


18.7 


21.1 


13.6 


17.5 


11.5 


10.8 


8.0 


7.0 


14L7 


7.1 


Aug. 9 


1.5 


0.8 


6.0 


1.3 


6.7 


4.0 


7.0 


5.9 


8.2 


9.6 


Aug. 31 






Continued heavy rains; no sa 


mples taken 






Wilting coeffi- 
























14.4 


14.7 


16.0 


14.1 


14.8 


13.6 


14.7 


16.3 


15.2 


15.9 


Hygroscopic 


















10.3 


10.8 


coefficient. . 


9.8 


10.0 


10.9 


9.6 


10.1 


9.2 


10.0 


11.1 



June was an unusually favorable month for crop growth. 8 to 16 per cent 
of available water occurred in the 0.5 to 5 foot soil-level, while drought con- 
ditions in the surface 0.5 foot were approached only during the latter part 
of the month, following the interval under consideration and when the grain 
was ripening (table 10). On June 3, soil temperatures in the oat plats at 
a depth of 0.5 to 2 feet ranged from 69° to 52° F. The graphs of soil and air 
temperatures, as well as that of humidity, indicate favorable growth condi- 
tions (fig. 20). Throughout the period the evaporation rate averaged about 
20 c. c. per day (table 11). 



46 Development and Activities of Roots of Crop Plants. 

Table 11. — Average daily evaporations at Lincoln, 1920. 



May 5 to 12 


ex. 

10.5 


June 30 to July 7 


ex. 


May 12 to 19 


14.9 


July 7 to 14 




May 19 to 26 


13.5 


July 14 to 21 




May 26 to June 2 


15.8 


July 21 to 28 




June 2to9 


15.9 


July 28 to Aug. 5 




June 9 to 16 


25.6 


Aug. 5 to 12 




June 16 to 23 


11.3 


Aug. 12 to 19 




June 23 to 30 


19.5 


Aug. 19 to 28 





»A11 atmometers, exept those at Peru, were equipped with the non-absorbing device. 

The roots had attained a maximum lateral spread of 0.8 foot, and a work- 
ing depth of 2.3 feet, while a few reached a maximum depth of 4.1 feet. A 
comparison of figures 19 and 21 A shows that the chief difference between 
the older root system and the younger, aside from greater length growth of 
most of the roots, is one of increase in number and branching of laterals. 
In fact, at the early stage (May 30), the general area to be occupied by the 
mature root system was well blocked out. Later it had been increased some- 







O 1. 












6 i 


3 e 


KJ 


7 


14 21 


28 


5 1 


2 1 


9 26 










/ 


\ 










/ 






























/ 

1/ 


I / 


I 

4 i 


/ 

t 


\ 

\ 


/ 




























V 

\ 


\/ 






/ 






J 


X 












/ 

— /_ 


✓ 


/ 

I— 


\ 


V 


-p 

/ \ 










\ 

1 


t 

\ 










-/< 




/ 
/ 
/ 
/ 


/ 

f 








V 


V 

\ 

\ 

— V- 






■> 


1 

i 

t 


\ 
\ 

1 


/ 


3k 

\ 
\ 

\ 







// 

7 — 


\ 


*~i 
1 












\ 

1 


t 
















J 


t 


"1 


1- 





























Fiq. 20.— Average daily air-temperature (long broken lines), soil-temperature (short 
broken lines), and humidity (solid line), 1920. 

what in width and considerably in depth, but especially it had come to be 
occupied much more thoroughly in all parts by a fine network of delicate 
roots. In the surface foot of soil, 7 to 10 laterals, and sometimes as many 
as 15 to 18, occurred on a single linear inch. On the scale to which the draw- 
ings were made it was very difficult to show all of the multitude of rootlets. 
The laterals were mostly 1 to 2 inches long, infrequently 3 to 5 inches, and 
were furnished only poorly with secondary branches. Branchlets of the 



Investigations at Lincoln, Nebraska. 



47 



third order were rare. In the second foot the branches became shorter, and 
not infrequently, for considerable distances, none were over 0.1 to 0.2 inch 
in length. Below 2.3 to 2.5 feet the number of roots decreased rapidly. 
While many of them were very poorly branched and often gave rise to only 
a few rootlets 0.1 to 0.5 inch long, in the course of several inches, most 
of them were branched quite regularly at the rate of 5 or 6 laterals per 
linear inch. These unbranched rootlets varied from 0.5 to over an inch in 
length. 

At this time a comparison was made with the development of oats in the 
lower crop plats. Due to a more fertile soil, as well as a more constant 
and greater supply of available water in the surface 0.5 foot (12 to 15 per 
cent), the crop was better developed (cf. tables 9 and 10). The plants which 
were beginning to blossom were 2.6 feet in average height, although some 
exceeded this by 0.5 foot. They had tillered more freely than the plants in 
the upland and the stand was thicker. The poorer stand and growth in the 
upland plats was probably due to the earlier planting and to differences in 
soil fertility and water-content. 

In the lowland area the maximum root depth (3.7 feet) was somewhat less 
than on the upland, although the working depth (2.7 feet) was greater. Little 
difference was determined in degree of branching or in lateral spread. 

The relatively slower development of the 1920 crop as compared with 
that of the more favorable growing-season of 1919 stands out strikingly. 
On June 12, 1919, 49 days after oats were planted, the crop in the upland 
area was 1.3 feet tall and had a working depth of 2.1 feet and a maximum 
depth of 2.8 feet. At the lowland station plants 1.8 feet high had roots with 
a working depth of 2.3 feet and a maximum depth of 3.3 feet (Weaver, 
1920 : 134). Thus plants only 49 days old, during this more favorable season, 
while not developed as far as the 80-day-old plants just described, were far 
beyond the latter at the age of 60 days. 

A final examination was made a few days after harvesting the crop on 
July 12. At this time the roots, except the deeper ones, were quite brittle 
and the cortex greatly shrunken, indicating that much material had been 
removed upward during ripening. Otherwise, the differences in the mature 
root system from that described at the beginning of the blossoming period 
are a somewhat greater working depth (2.7 to 2.8 feet) and an even more 
thorough occupation of the soil-mass already delimited at the earlier exami- 
nation. 

The period June 20 to July 12 was one very favorable for root growth. 
Several well-distributed rains furnished an abundant water-supply to the 
surface soils, while the deeper layers had 8 to 16 per cent of water constantly 
available. On the lower crop-plats, moisture conditions were also favorable 
(table 10). Here the roots of the matured plants had penetrated to maximum 
depths of 4.3 to 4.8 feet, but the working level (2.8 feet) had changed little 
since the previous examination 24 days earlier. Allowing for differences in 
soil condition (although all root excavations in any plat were made within 
a radius of a few meters), these findings agree only in part with those of 
Rotmistrov (1914 : 24) that " towards the commencement of flowering the 
development of the root system finishes, or the growth of the roots after 
that to the attainment of maturity is insignificant." 



48 Development and Activities of Roots of Crop Plants. 

The grain yield of the crop-plats was not determined. 20 or 30 quadrats 
were selected from each plat (Kiesselbach, 1918), and the total dry weight 
of tops, including grain, obtained (cf. p. 76). 

The extent of shoot and root of the oats in both upland and lowland areas 
during 1919 was almost identical with that of 1920, although the crop in 
1919 reached maturity at the end of 75 days. 

Barley, Hordeum vulgare. 

The root development of barley growing in an adjoining plat was deter- 
mined, as was also that of wheat, at the same intervals as for oats. At the 
first examination, on May 1, the evenly developed crop had a height of 2.5 
to 3 inches. Nearly all of the plants had a second leaf 1 to 2 inches long. 
The general root habit as regards fineness of roots, branching, and lateral 
spread is almost identical with that of wheat and oats, being somewhat inter- 
mediate between the two. The maximum depth of root penetration was 
10 inches and unbranched laterals 0.3 to 1 inch in length were fairly abundant, 
except near the root ends. 

On May 15 the plants averaged 4.5 inches in height, some had 2 or 3 tillers 
with the second leaf unfolding, and practically all had developed 3 or 4 leaves. 
Plants of average size had from 5 to 11 roots. The longest reached a depth 
of 2.2 feet, but most of them ended at about the 1.2-foot level. The general 
working depth of the root system was 9 inches and the maximum lateral 
spread 8 inches. The older portions of the root system were well furnished 
with primary laterals varying in length from 1 to 1.5 inches, some of which 
had secondary branchlets 0.3 inch or less in length. Young, entirely un- 
branched roots ran off horizontally or obliquely to distances of 1 to 3 inches. 
Where roots entered crevices in the soil, they were densely covered with 
short branches and root-hairs. Below 11 inches only a few short branches 
occurred. As in the other cereals studied, the glistening-white, deeper roots 
often ran several inches without branching. 

An examination of the development of barley on June 3 showed that the 
plants had made a marked growth of both tops and roots. They averaged 
8 inches tall, although some were 11 inches. 5 or 6 leaves had developed on 
each plant, and many had 1 to 3 tillers, the oldest being from one-third to 
one-half as tall as the parent. The area to be occupied by the mature root 
system was at this time fairly well delimited, except in depth. Of the 10 to 
17 main roots on a plant, some descended only slightly outward and then 
downward to a depth of 1.7 to 2.7 feet, the deepest reaching 3.2 feet. Many 
others extended rather horizontally or obliquely for horizontal distances of 
5 to 8 inches from the plant, the shallowest ending in the surface 3 inches of 
soil. Thus, barley roots are somewhat nearer the surface at this stage than 
wheat or oats. The most superficial, younger roots, and indeed nearly all 
of those in the surface 1 or 1.5 feet of soil, were clothed with an abundance of 
laterals, often as many as 15 per inch, and an inch or less (rarely more than 
2 inches) long. Below 1.5 feet laterals were far less abundant, rather irregu- 
larly distributed (3 to 8 per inch), and also much shorter. Secondary lat- 
erals were in no case abundant, although some from a few millimeters to an 
inch in length were found. The last 6 to 12 inches of the rapidly growing 
roots, and especially the deeper ones, were entirely devoid of branches. 



Investigations at Lincoln, Nebraska. 



49 



The soil area thus inclosed by the developing root system was only fairly 
well occupied at this time to a working level of about 1.8 feet. 

Barley plants at Peru, 54 days after planting, gave a greater height growth, 
while maximum root penetration exceeding that of these 63-day-old plants 
by 1.3 feet. Moreover the differentiation of the root system into two parts 
was rather clearly marked (p. 18). 

Plants 80 days old were examined on June 19 and 21. They averaged 2.3 
feet in height, with a maximum development of 2.7 feet. Many plants had 
no tillers, others had 1 to 7, with an average of about 2 or 3. The crop was 
just beginning to blossom. A great tangle of well-branched roots spread 
laterally from medium-sized plants to distances of 7 to 10 inches and occu- 
pied the soil thoroughly to the working level at 2.7 feet. Even below this 
level roots were quite abundant for 8 or 10 inches, the longest extending to a 
total depth of 4.4 feet. Roots were more abundant in the surface 3 inches of 
soil than were those of either wheat or oats. The development of secondary 
rootlets was very similar to that of oats and wheat. Wheat, however, was 
found to be more abundantly supplied with finer rootlets than either oats 
or barley. 

In the lowland plats, at this time, the crop was about 2.7 feet in average 
height and had been in blossom for 2 or 3 days. The working depth of the 
roots was 3 feet, while the longest reached the 4.5-foot level. The greater 
abundance of surface roots as compared with wheat and oats was clearly 
evident. 

A final examination of the root system, shortly after the grain was harvested 
on July 12, showed, as in the case of the other cereals, that the working level 
was somewhat deeper (2.9 feet), as was also the maximum depth (4.7 feet); 
The area of soil under the plants was even more completely filled with great 
masses of finely branched roots, the whole forming an exceedingly efficient 
absorbing system. On the lowland area the roots of mature barley plants 
had a working depth of 3.3 feet, while several of the longer roots were traced 
to depths of 5.4 feet. 

Wheat, Triticum ^estivum. 

The root development of Marquis Spring wheat, growing in an adjoining 
plat, was determined at the same intervals as the oats. On May 1 the wheat 
had an average height of 2.5 inches, although many plants were an inch 
taller. The stand was good and the crop quite evenly developed. The sec- 
ond leaf was from 1 to 3 inches long in nearly all plants, while some were 
unfolding the third leaf. The root system, while very similar to that of 
oats, was somewhat more extensive. The number of roots on the large lot 
of plants examined varied from 3 to 8, with an average of about 6. The maxi- 
mum depth of penetration was 15 inches, although most of them were much 
shorter, so that the working depth was only about 6.5 inches. The greatest 
lateral spread was 5 inches. The root diameter, which was almost identical 
with that of oats and barley, was seldom over 0.5 mm. Laterals occurred 
at the rate of about 5 to 13 per inch. These varied in length from only 2 
mm. to 1.3 inches. They were entirely unbranched. On the youngest por- 
tions of the roots practically no laterals occurred, but as a whole they were 
somewhat more numerous than on the oats or barley (fig. 22). Environ- 



50 



Development and Activities of Roots of Crop Plants. 



mental conditions during the several intervals of growth have already been 
given in the discussion of oat. It is of interest to note that wheat planted 
May 15 was further developed after a growth period of 15 days than were the 
31-day-old plants just described. The former were 3 or 4 inches tall, had 
unfolded 3 leaves, and the roots were developed proportionally. But even 
these had not made the rapid root growth recorded by Rotmistrov (1909 : 33). 

Plants 45 days old were examined on May 15. The crop had an average 
height of 4 inches, the tallest plants exceeding this by only 0.5 inch. Some 
plants had 2 or 3 tillers, the largest of these offshoots having 2 or 3 leaves. 
The root development again execeded that of oats, with a maximum depth 
of 2.3 feet, a general working level of about 10 inches, and an extreme lateral 
spread of 8 or 9 inches (fig. 23 a). 8 to 10 roots per plant were commonly 
found; many new roots only 1 or 2 inches in length occurred on the plants 
that were tillering. In the surface 6 or 8 
inches of soil, lateral roots 1 to 3 inches 
in length and many more shorter ones were 
found. These had a few very fine second- 
ary laterals only a few millimeters long. 
Below 10 inches the main roots became 
glistening white, larger in diameter, and 
the laterals very sparse. As a whole, wheat 
roots are somewhat finer and more thread- 
like than those of oats or barley. Wheat 
planted May 5, when 25 days old, showed 
more advanced growth than these. It had 
reached a height of 4 or 5 inches, was de- 
veloping the fifth leaf, and had tillers with 
2 or 3 leaves. A third examination of 
wheat was made on May 29 and 31, when 
the plants, now 60 days old, had reached 
an average height of about 8 inches and 
had grown 4 to 6 leaves. A few plants 
were 12 inches tall. Nearly all had 2 or 3 
and some 4 to 7 tillers; the largest of these 
had 3 or 4 leaves. The roots, during the Fig. 22.— wheat 31 days old. 
15-day interval since the last examination, 

had increased to a total of 11 to 18 per plant. Many penetrated deeper than 
before, others spread obliquely downward, and, with the increase of laterals 
both in number and length, began to fill in the soil area already delimited at 
the earlier stage. The average maximum root penetration was 2.6 feet, but a 
few roots ended 5 inches deeper. The last 8 to 12 inches of root in the very 
moist subsoil were glistening-white, ran vertically downward, and were not 
only free from branches, but, like the deep oat roots, were not well clothed with 
root-hairs. The working depth was about 1.5 feet. The maximum lateral 
spread was about 10 inches, although few roots spread so widely (fig. 23 b). 

Further studies were made on June 19 and 21, when the crop was in blos- 
som. The plants averaged about 2.2 feet in height, the tallest reaching 2.8 
feet. The number of tillers per plant varied from single-stemmed plants to 
those with 7 or 8 tillers, but the average was about 2. 20 days of growth had 




Investigations at Lincoln, Nebraska. 



51 




Fig. 23.— A. Wheat 45 days old. B. Wheat 60 days old. 



52 Development and Activities of Roots of Crop Plants. 

shown a profound development of the root system. The working level had 
reached a depth of 2.8 to 3.1 feet; the longest roots penetrated the soil rather 
vertically downward for 4.8 feet; the lateral spread had increased to a maxi- 
mum of about 1 foot, while a vast network of rebranched laterals occupied an 
area of soil extending roughly 0.8 foot on all sides of the plant and to a depth 
of 2 or 3 feet (fig. 21 b). The total number of roots had now increased to 
20 or 25, varying with the number of tillers on a parent plant. Many of 
these were more superficially placed than in earlier stages of development, 
running off rather horizontally or obliquely and ending in the first 3 to 8 
inches of soil. In the surface 2 feet especially, laterals were exceedingly 
abundant, usually 5 to 9 occurring on an inch of root-length. Many of these 
were short and few exceeded 3.5 or 4 inches in length. Secondary laterals 
were not at all abundant. In the second foot the branches were mostly less 
than an inch in length. Below 2 feet branching was somewhat less pro- 
nounced, especially as regards length of primary rootlets and abundance of 
secondary ones. In the fourth and fifth foot numerous roots were charac- 
terized by unbranched laterals about 0.3 inch in length, but only 1 to 4 oc- 
curred on an inch of root. On others the branches were much thicker but 
shorter, and frequently occurred to within an inch of the root-ends. Again, 
other root-ends were without branches for several inches back from their tips. 

In the lower plats the wheat at this time was 2.6 feet tall and blossoming 
had just begun. As with the other cereals, tillering was much more pro- 
nounced (average of 3.2 stems per plant as compared with only 1.7 in the 
upland) and the stand was thick. The maximum root penetration was 4.8 
feet and the working depth about 3.1 feet. No marked differences were 
noted in the branching habit or extent of lateral spread. 

A final examination a few days after harvesting the grain on July 15 
showed no great change in root development. As with oats and barley, the 
roots, except the deepest ones, were somewhat shriveled and more brittle 
than before. The depth and lateral spread had increased only slightly. In 
the lower crop plats the working level had deepened to 3.5 feet, but no roots 
were found below the former 4.8-foot level. As a whole, the root system 
was a little finer and somewhat more extensive than that of oats. 

Alfalfa, Medicago sativa. 

This crop was sowed on the upland plats on March 31, in an area adjoining 
the cereals. The environmental conditions until May 1, when the initial 
examination of root development was made, have already been described 
(p. 42). At this time the plants were not over 0.5 inch in height. The first 
pair of true leaves was just unfolding. The tap-roots had penetrated to 
depths of 5 or 6 inches and the first laterals were just beginning to form on 
some plants. 

A second examination was made on June 2. The plants averaged only 
2.5 inches in height, although certain individuals exceeded this by 0.5 to 1.5 
inches. The stage of development of both tops and roots is shown in figure 
24 a. Several roots reached depths of 1.5 feet, while two of the plants exam- 
ined had roots 1.8 feet long. Practically no branches occurred in the surface 
1 or 1.5 inches of soil, but below this level as many as 10 or 12 per linear 
inch of tap arose. These varied from a few millimeters to 3 inches in length; 



Investigations at Lincoln, Nebraska. 



53 



the longer ones had a few secondary laterals, mostly less than 0.4 inch long. 
On smaller plants nearly all of the laterals were less than 0.5 inch in length 
and extended out in a more or less horizontal direction or turned somewhat 
obliquely downward. On all roots the 2 to 4 inches nearest the tip were 
glistening white and unbranched. Nodules were abundant. 

A third examination of the root development was made July 24 on both 
upland and lowland areas. The plants were 115 and 106 days old respec- 




Fig. 24. — A. Alfalfa 63 days old. B. Sweet clover 63 days old. 



tively. Those in the upland area averaged 1.1 feet in height, the tallest reach- 
ing 1.4 feet. They had developed normally in every way, but were somewhat 
affected by " white spot." On the lowland the crop averaged 1.7 feet high, 
the tallest plants reaching 2 feet. It has already been pointed out (p. 45) 
that June was a very favorable month for growth. Excellent growth con- 



54 



Development and Activities of Roots of Crop Plants. 



ditions also prevailed throughout July. Well-distributed rains furnished 
abundant soil-moisture (table 10); soil and air temperatures and humidity 
were favorable (fig. 20), and evaporation was not excessive (table 11). 

The roots on the upland had penetrated to a maximum depth of 5.2 feet 
and were fairly abundant to the 4.2-foot level. Those on the lowland were 
slightly deeper. The greatest depth of penetration was 5.7 feet and several 
occurred at the 5-foot level. In both areas the tap-root was the prominent 




A Ei 

Fig. 25. — A. Alfalfa 132 days old. B. Sweet clover 115 days old. 

feature, varying from 3 to 5 mm. in diameter. Laterals were not abundant 
below the surface 1.5 foot of soil. The longest did not exceed 6 or 8 inches. 
The roots penetrated nearly vertically downward and were furnished at irreg- 
ular intervals with short, mostly poorly branched or unbranched rootlets. 
These occurred at intervals of an inch or less, becoming smaller near the 



Investigations at Lincoln, Nebraska. 



55 



tip. Nodules occurred to depths of over 3.5 feet. Little difference was noted 
in the number or length of branches of roots excavated in the lowland. 

A final examination in the upland plats was made on August 10. At this 
time the tallest plants were 1.5 feet high, while the crop averaged 1.3 feet. 
Growth conditions had continued favorable, soil-moisture was abundant, 
especially in the deeper layers, and root growth continued. Many of the 
roots had reached a depth of 5 feet, while some penetrated 2 to 6 inches 
deeper. The tap continued to assume the dominant role, and no change 
occurred in branching habit. The older laterals were longer and extended 
laterally often more or less parallel with the soil-surface for distances of 6 to 
10 inches or turned obliquely downward, usually making wide angles with 
the tap (fig. 25 a). Root development in both upland and lowland areas 
during 1919 was very similar to that just described (Weaver, 1920 : 127). 

Sweet Clover, Melilotus alba. 

This crop was planted on the same day as alfalfa (March 31) in level plats 
adjoining those of the cereals. On May 1, when the plants had reached a 
maximum height of 0.5 inch, the root systems were examined. None of the 
roots reached depths greater than 3 or 4 inches. 

A second examination was made on June 2, when the crop was 1.5 to 2 
inches tall. Many roots extended to depths of 0.9 to 1.2 feet and a few 
reached the 1.4-foot level. Secondary laterals were fairly abundant, as were 
also the bacterial nodules. The branching habit was very similar to that of 
alfalfa of the same age (cf. figs. 24 a and 24 b). 

On July 24, when the crop had reached an average height of about 1.3 
feet, root development was again examined. Roots were abundant to the 
5-foot level, while some penetrated the moist soil to a distance of 5.5 feet. 
On the lowland, where the tops were better developed (average height about 
2.2 feet) the root development was almost identical as regards depth of pene- 
tration, abundance of branching and lateral spread, and presence of nodules 
at all depths. The strong tap-roots varied from 4 to 6 mm. in diameter, 
penetrated almost vertically downward, and tapered rapidly. Ma j or branches 
were few, usually only 1 to 3 per plant. These originated at various depths, 
sometimes near the surface and again as deep as 2 or 3 feet. Like the main 
root, these larger branches, sometimes 2 or 3 feet long, were furnished with 
rather numerous relatively short and mostly poorly branched sublaterals. 
The most marked development of laterals on the tap occurred in the surface 
foot of soil. No branches extended to horizontal distances greater than 8 
or 10 inches from the tap and most of them were very much shorter (fig. 25 b). 

Comparison of Root Systems. 

Just as the native species examined in the prairies at Peru were found to 
be more deeply rooted than those at Lincoln (Weaver, 1919 : 15), so too the 
crop plants show clearly this difference in root habit. Table 12 summarizes 
the development of the crops at Lincoln. When this is compared with a 
similar summary for the Peru crops (table 1), striking differences are at once 
apparent. Oats at Peru reached a maximum depth of 6.7 feet, at Lincoln 
only 4.2 feet. The maximum lateral spread was 1.4 feet at the former sta- 
tion and only 0.8 foot at the latter. Differences in the root development of 



56 



Development and Activities of Roots of Crop Plants. 



Marquis wheat and barley were scarcely less striking, the greater development 
of the root system at Peru being consistent for all crops examined. Nor is 
this difference correlated with height-growth, for the average height-growth 
of the several crops at Lincoln during 1919 and 1920, especially when the 
lowland plats are included, was not unlike that at Peru. Moreover, the 
differentiation of root systems into a more or less distinctly shallow portion 
and a more deeply penetrating one was much more marked at the latter 
station. The root habit of the cereals at Lincoln was consistent during the 



Table 12. — Development oj upland crops at Lincoln, Nebraska, 1920. 





Age 


Aver- 


Stage 


Work- 


Maxi- 


Maximum 




Crop. 


of 


age 


of 


ing 


mum 


lateral 


Remarks. 


plants. 


height. 


development. 


depth. 


depth. 


spread. 






days. 


feet. 




feet. 


feet. 


feet. 






31 


0.2 


1 or 2 leaves . 


0.4 


0.7 


0.3 


5 to 7 roots. 


Oats, 


45 


0.3 


4 leaves 


0.7 


2.0 


0.5 


7 to 14 roots; no tillers. 


White 


60 


0.7 


7 to 9 leaves . 


1.5 


2.7 


0.7 


16 to 27 roots; to 2 tillers. 


Kherson 


80 


2.0 


In blossom. . 


2.3 


4.1 


0.8 


to 5 tillers per plant. 




103 


2.0 




2.7 


4.2 


0.8 






31 


0.2 


2 or 3 leaves . 


0.5 


1.3 


0.4 


3 to 8 roots. 


Wheat, 


45 


0.3 


4 leaves 


0.8 


2.3 


0.7 


8 to 10 roots; to 3 tillers. 


60 


0.7 


5 or 6 leaves . 


1.5 


3.0 


0.8 


11 to 18 roots; 2 to 7 tillers. 


Marquis 


80 


2.2 


In blossom. . 


3.0 


4.8 


1.0 


20 to 25 roots; to 8 tillers. 




106 


2.2 




3.2 


5.0 


1.0 






31 


0.2 




0.5 


0.8 


0.4 


3 to 7 roots. 




45 


0.4 


3 or 4 leaves . 


0.7 


2.2 


0.7 


9 roots; a few tillers. 


Bailey, 


63 


0.7 


5 or 6 leaves . 


1.8 


3.2 


0.7 


10 to 17 roots; to 3 tillers. 


Manchuria 


80 


2.3 


In blossom. . 


2.7 


4.4 


1.0 


to 7 tillers. 




103 


2.3 




2.9 


4.7 


1.0 





years 1919 and 1920, both of which, except for a late, cold spring in 1920, had 
growing-seasons very favorable for crop development. Just how much the 
modification of the root habit at Peru was due to the drought which prevailed 
during 1919, and how much it was affected by other factors, such as soil 
texture, fertility, etc., will be further discussed when the 1921 root growth 
at the several stations is compared in chapter 5. A summary of earlier inves- 
tigations on the root development of crop plants in the true prairie may be 
found in chapters 6 and 7 of " Root development in the grassland formation.' ' 



Investigations at Phillipsburg, Kansas. 



57 



III INVESTIGATIONS AT PHILLIPSBURG, 
KANSAS, IN 1920. 

A third station was maintained during 1920 at Phillipsburg, in north-central 
Kansas. This station which is about midway between Lincoln, Nebraska, and 
Burlington, Colorado, has an altitude of 1,935 feet and an annual precipita- 
tion of 23 inches. The crop plats occupied an area, quite typical of the rolling 
topography, on a hillside which sloped gently to the south and east. 

The fertile soil is a mellow dark-brown silt-loam of the Colby series. At 
a depth of 1 to 1.2 feet it is slightly lighter in color and contains enough clay 
to be quite sticky, although when wet it is dark in color to a depth of 2 feet. 
Below this level it is light yellow, and shows throughout its loess origin. 
The first 4 feet have a water-holding capacity of about 66 per cent. Excava- 
tions for root examinations near this station on June 27, 1919, showed that the 
soil was thoroughly moist to a depth of at least 8 feet and repeated excavations 
in the plats during 1920 failed to reach the limit of water penetration. 

The crops grown here were from the same lot of seed as that used at 
Lincoln and Burlington. Moreover, the methods and rate of seeding, etc., 
were the same as those employed at the other stations. The field had been 
broken for several years; the preceding crop was wheat. It was plowed to a 
depth of about 5 inches, harrowed, and brought to good tilth before the crops 
were hoed in on May 7. The late date of planting, unavoidable because of 
weather conditions, should be noted, since it bears a close relation to the 
later maturing of the crops and the injury done by a rust epidemic. 

Oats, Avena sativa. 

The first examination of root development was made on June 10. The crop 
was in a thriving condition, and, although only 34 days old, had reached an 
average height of 9 inches. The parent plants had 5 or 6 leaves each and had 
tillered rather freely. Many had 2 or 3 tillers each. Some of the offshoots 
were of equal or nearly equal height with the parent plants, while others were 
only 1 or 2 inches high. The stand was quite uniform and the plants of 

even height. . 

The period as a whole had been one favorable to rapid growth, and, m tact, 
the crop was as far developed as the oats at Lincoln at the age of 55 days 
(i e on May 25). At the time of seeding 16 per cent available water was 
present in the oat plats in the first 2 feet of soil and 11 or 12 per cent to a 
depth of 4 feet. Frequent, well-distributed showers during the remainder 
of May, totaling 3.4 inches, kept the soil in good condition. On June 2, 
12 per cent available water was present to 4 feet depth, except that the surface 
6 inches had only 10 per cent. Similar water-content conditions prevailed 
until June 10 (table 13). 

The temperature of the soil from June 2 to 10 varied from 59 to 16 b. at 
a depth of 6 inches, with an average daily temperature of 65° F. The air- 
temperature during the same interval varied from 51° to 90° F. with a mean 
of 69° F. The mean air-temperature for May was 60.6° F. The evaporating 
power of the air (June 2-10) was only 11 c. c. daily. 

An examination of the roots showed that they had made a good growth and 
were remarkably similar in development and distribution to those of the crops 



58 



Development and Activities of Roots of Crop Plants. 



grown at Lincoln. In fact, the similarity was so great in case of the cereals 
that detailed descriptions need not be given. The lateral spread was about 
5 to 7 inches. The working depth was 2.1 feet. One root was traced to a 
maximum depth of 3.8 feet and several were found at the 3.5-foot level. 
Below 2.6 feet the thick, white roots were entirely devoid of branches. Thus 
the root system was more deeply seated than that of oats at Lincoln on May 30. 

Table 13. — Water-content in excess of hygroscopic coefficient in crop plats at Phillipsburg , 

Kansas, 1920. 



Date. 


to 0.5 foot. 


0.5 to 1 foot. 


1 to 2 feet. 


2 to 3 feet. 


3 to 4 feet. 


May 7 


16.8 


16.7 


15.8 


12.6 


11.0 


June 2 


9.7 


12.2 


12.7 


12.8 


12.4 


June 10 


9.1 


13.0 


11.2 






June 24 


8.5 


7.6 


9.0 


10.3 




July 1 


-0.4 


0.9 


2.9 






July 9 


-3.1 


2.5 


0.9 


1.3 


3l9 


July 21 


-3.3 


-1.2 


-0.4 


0.4 


0.9 


Aug. 4 


2.3 


4.0 


2.5 


2.2 


2.1 


Aug. 26 


0.1 


1.5 


-2.1 


-0.9 


0.9 




13.3 


13.3 


13.4 


13.5 


13.1 


Hygroscopic coefficient. 


10.6 


10.6 


10.9 


10.6 


10.7 



On July 9 the oats was well past the dough stage of grain development. 
The crop averaged 2.6 feet in height. Counts on selected square-meter areas 
showed that the plants had an average of 2.3 tillers each. The crop was 
slightly damaged by grasshoppers and also somewhat affected by stem rust, 
Puccinia graminis avence. Indeed, by the time of harvest (July 20) the rust 
epidemic was so severe that the grain was very light and of very poor quality. 

Table 14. — Average daily evaporation at Phillipsburg, Kansas, 1920. 



June 2 to 10 11.0 

June 10 to 17 26.9 

June 17 to 24 12.3 

June 24 to July 1 24 . 5 

July 1 to 8 32.2 

July 8 to 15 30.6 



July 15 to 21 25.9 

July 21 to 28 29.5 

July 28 to Aug. 4 21.1 

Aug. 4 to 11 13.8 

Aug. 11 to 18 13.0 

Aug. 18 to 26 24.2 



The root system by this time had penetrated the loess soil to a working 
depth of 3.3 feet. A maximum depth of 6 feet was recorded for a few of the 
longest roots, while at 5.5 feet depth they were not at all uncommon. Thus, 
the root depth exceeded that at Lincoln (4.2 feet) and nearly equaled that 
at Peru (6.7 feet). The root extent was greater than that of Texas Red oats 
(4.8 feet) excavated a few miles distant, but in similar soil, in June 1919 
(Weaver, 1920 : 119). 

The clue to this marked root development is apparently to be found in 
an examination of the texture and water-content of the soil and the aerial 
conditions causing water-loss. In general, the mellow soil during this interval 
was relatively dry when compared with conditions at Lincoln, while the 
evaporating power of the air was greater than at the latter station. This 
seems to have stimulated root-growth in the deeper soils where available 



Investigations at Phillipsburg, Kansas. 



59 



water was present. Only 1.96 inches of rain fell during this period (June 10 
to July 9), and about 20 per cent of this occurred in 9 light showers which had 
little or no appreciable effect upon water-content. An examination of table 
13 reveals the scarcity of available moisture, which was entirely exhausted 
from the surface 6 inches of soil on July 1 and 9. Throughout the period the 
evaporating power of the air was relatively high, about 24 c. c. daily (table 14). 
The average daily air-temperature ranged from 64° to 76° F., maximum 
temperatures of 88° to 99° F. not being unusual. The soil-temperature at 6 
inches depth varied from 65° to 77° F. (fig. 26). 



June July August 

2 34 1 23 4 1 23 4 



























\> \ 


/ // 


















/ / 
I / 
1/ 


\\ V 

\N \ 
\ \ 


/ * / 

r/ / 

'/ 



















Fig. 26. — Average day and average night air-temperatures and average 
daily soil-temperature (broken line) at Phillipsburg, 1920. 



Barley, Hordeum vulgare. 

On* June 10, when the barley roots were first examined, the crop was in good 
condition and had an average height of about 10 inches. The parent plants 
had from 4 to 6 leaves each. They frequently had 3 to 5 tillers, and some 
of these were almost as tall as the original shoot. The stand was fairly even 
and the plants of uniform height. The roots had a working depth of 2.5 feet, 
a lateral spread of about 0.5 foot on all sides of the plant, and reached a maxi- 
mum depth of 4.3 feet. 

A second examination was made on July 9, when the crop was 2.4 feet high 
and in the dough stage of development. It was badly affected by stem rust, 
Puccinia graminis tritici, and the grain, when ripe, was light and wrinkled. 
The root system had a working depth of about 3.3 feet; several roots were 
traced to a depth of 6 feet and a few even to 6.7 feet. Root habit as regards 
lateral spread, degree of branching, etc., was nearly identical with barley 
grown at Lincoln. 

Wheat, Triticum ^estivum. 

At the time of the first examination (June 10), the Marquis Spring wheat 
was about 7 inches in average height and of good, even stand. It had tillered 
more freely than either of the other cereals, 6 offshoots not being uncommon. 
Some of the tillers were as tall as the parent plants, and, like them, had 4 or 
5 leaves each. The crop was not only shorter above ground than the other 
cereals, but the root system was much more poorly developed. The working 
depth was only 2.1 feet (compared with 2.5 feet for barley), while practically 
no roots penetrated beyond the 3.7-foot level. 

On July 9, when again examined, the crop was 2.3 feet in average height. 
The wheat was badly rusted, and the grain, now beyond the dough stage, was 
shriveled and light when harvested on July 20. The surface-rooting habit 
was similar to that at Lincoln, the roots having a maximum lateral spread of 
a foot. The working level now reached 3 feet, while maximum root penetra- 



60 Development and Activities of Roots of Crop Plants. 

tion was about 5.8 feet. The long, glistening-white, unbranched root-ends 
in the deeper soil were very characteristic. The soil was quite moist to 
all depths examined, about 8 feet. 

Alfalfa, Medicago sativa. 

The root development of this crop was studied at the same time as that of 
the cereals. On June 9 the plants were from 4 to 5 inches in height and grow- 
ing vigorously. The stand was fairly uniform. Numerous tap-roots were 
found terminating at depths of 2 to 2.7 feet and the soil was well filled with 
roots to the 1.3-foot level. Tubercles were abundant. The branching 
habit, number of laterals, etc., were so nearly identical with that described 
at Lincoln that further description is unnecessary (cf. fig. 24 a). 

By July 10 the larger alfalfa plants were 14 inches tall and in good condition; 
a few were beginning to blossom. Although the surface 1.5 feet of soil was 
quite dry, the deeper soil was moist to the maximum depth of root penetration, 
about 5 feet, and, in fact, for several feet beyond. As at Lincoln, the absence 
of large lateral branches was a characteristic feature of the root habit, which 
agreed in all essentials with plants of similar age described at the former station. 

Sweet Clover, Melilotus alba. 

When sweet clover was first examined (June 10), the tallest plants were only 
3 inches high and the average height of the crop was only 2 inches. However, 
the underground parts were well advanced in development. The surface 1.7 
feet of soil was well filled with roots and an average maximum depth for many 
plants was 2.5 feet. Two especially deep ones penetrated to the 3-foot level. 
All of the numerous laterals, which were similar to those at Lincoln in number 
and extent, were well supplied with nodules. 

On July 9, when the crop had reached a height of 1.3 to 1.7 feet, a second 
examination was made. The above-ground parts were greatly exceeded in 
extent by roots. Some of the larger tap-roots were 6 or 7 mm. in diameter 
and reached depths of 4.5 to 5.7 feet. The long, vertically descending, and 
unbranched root-ends were developing rapidly in the moist subsoil (cf. fig. 25 b). 

Summary of Crop Development. 
The crops at Phillipsburg were planted later than at the other stations and 
before harvest were badly injured by a rust epidemic which materially re- 
duced the yield. Early spring conditions were favorable to growth and the 
stand in every case was quite uniform, the cereals tillered well, and the crops 
developed rather uniformly and more rapidly than those planted earlier at the 
other stations. Oats, wheat, and barley, when matured, averaged 2.6, 2.3, 
and 2.4 feet in height respectively, while the height of alfalfa and sweet clover 
was 1.2 to 1.7 feet. Responding, apparently, to the environment during 
June and July, which coupled high water-loss with a relatively dry surface-soil, 
the crops developed root systems which extended far into the deeper moist 
soils. Thus, the roots of wheat and oats penetrated to about 6 feet and those 
of barley even deeper. Alfalfa and sweet clover, when only 64 days old, 
reached depths exceeding 5 feet. The abundance of laterals, degree of branch- 
ing, and general root habit corresponded otherwise with crops grown in less 
arid regions. These results are not at variance with those obtained at the 
same and neighboring stations during 1919, and also check well with the 
root habits of the native mixed-prairie vegetation. 



Investigations at Burlington, Colorado. 



61 



IV. INVESTIGATIONS AT BURLINGTON, 
COLORADO, IN 1920. 

Crops were also grown during 1920 at Burlington, a station in the short- 
grass plains of eastern Colorado, having an altitude of 4,160 feet and an 
average annual precipitation of 17 inches. The crops which were from the 
same lot of seed as that used at Lincoln, were planted at the same rate per 
acre and in the same sized plats as those described. In fact, except for the 
normally later sowing (April 15) due to a later spring at the higher altitude, 
the experimental plats were duplicates of those at the former station. The 
soil is a rich, brown, fine sandy loam, very compact and hard when dry. It 
has a water-holding capacity of 65 to 70 per cent to a depth of 4 feet. At a 
depth of 2 to 2.5 feet it is underlaid with a so-called hardpan. Soil analyses 
show that the concentration of colloidal clay and carbonates in the subsoil 
is sufficient to give rise to a hardpan, i. e., a much more compact stratum 
of soil relative to that above or below it, upon its becoming completely 
dried out (Weaver and Crist, 1922). An examination of table 15 shows 
that silt constitutes about one-third of the soil at all depths, while the sand 
decreases and the clay increases in amount to 4 feet. 



Table 15. — Mechanical analyses of soils from Burlington, Colorado. 







Depth of sample, in 


feet. 






0.0 to 0.5 


0.5 to 1.0 


1 to 2 


2 to 3 


3 to 4 




p. ct. 
0.0 


p. ct. 
0.0 


p. ct. 
0.0 


p. ct. 
0.0 


p. ct. 
0.0 




0.0 


0.0 


0.0 


0.0 


0.0 




0.0 


0.0 


0.0 


0.0 


0.0 




0.13 


0.14 


0.17 


0.13 


0.10 




2.6 


2.2 


1.9 


1.5 


0.9 




48.6 


49.1 


46.7 


45.5 


42.2 




33.4 


32.5 


32.0 


31.0 


34.2 


Clay 


15.3 


16.1 


19.3 


21.9 


22.6 


Hygroscopic coefficient. . . 


10.9 


10.9 


12.2 


12.0 


11.4 



Chemical analyses show that carbonates are practically absent in the 
surface soil, but increase rapidly with depth, and in the hardpan layer, which 
appears somewhat chalky in color, they often reach concentrations of 5 or 6 
per cent. Table 16 shows that the soils are not acid, the carbon dioxide 
increasing very rapidly with depth and being very high at 2 to 4 feet. These 
soils are rich in phosphorus and potassium and have a sufficient supply of 
nitrogen. Thus, all the critical elements are present in abundance. 

Hardpan is found rather generally throughout the short-grass plains asso- 
ciation. The native short-grasses compact the soil so firmly that run-off 
is usually high, while the water penetrates very slowly. This is indicated 
by the frequent occurrence of dry stream-beds of various sizes. Shantz 
(1911) has shown that the average run-off from the short-grass sod at five 
stations in this region was 37 per cent of the total rainfall (maximum 55 per 
cent), while that from variously tilled crop areas was almost as great. After 



62 Development and Activities of Roots of Crop Plants. 

heavy rains three days were required for the water to penetrate to a depth 
greater than 6 inches. This high run-off has been repeatedly confirmed by 
the writers while the penetration of water, when applied to moisten the sur- 
face soil prior to root examinations, was exceedingly slow. The excellent 
root development of native plants in the surface 1.5 to 2.5 feet of soil fits them 
to absorb the water readily, and they help to prevent deep water penetration 
(Weaver, 1919, 1920). This is of especial significance in this study, since 
cultivated plants modify their root distribution in a manner similar to that 
of the native vegetation. 



Table 16. — Chemical analyses of soils from Burlington.* 







Depth of sample in 


feet. 




0.0 to 0.5 


0.5 to 1.0 


1 to 2 


2 to 3 


3 to 4 




p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 




none 


none 


none 


none 


none 


Carbon dioxide 


0.03 


0.30 


1.71 


2.10 


2.60 




4.67 


3.13 


3.11 


3.34 


2.84 


Phosphorus pentoxide .... 


0.189 


0.504 


0.428 


0.406 


0.525 


Sulphur trioxide 


0.007 


0.017 


0.006 


0.006 


0.005 


Potassium oxide 


2.32 


2.39 


2.45 


2.51 


2.22 




0.184 


0.130 


0.101 


0.086 


0.084 



1 Methods used were the same as described on p. 32. 



The field in which the crop plats were located was a portion of a vast level 
tract surrounded on three sides by fields of wheat, corn, and Sudan grass, 
respectively. The sod had been broken in the spring of 1918 and planted to 
Sudan grass. After this was harvested the ground was plowed late in the 
fall, and the next spring it was repeatedly harrowed and a good seed-bed 
formed before the experimental crops were hoed in. 

Wheat, Triticum ^estivum. 

On June 12, 58 days after planting, the Marquis Spring wheat was thor- 
oughly examined. The plants averaged 10 inches in height, the tallest 
reaching 12 inches. They were well-tillered, many having from 4 to 8 
shoots. The parent plants had an average of about 6 leaves each. Many of 
the tillers were 6 to 10 inches high, but others were only 1 or 2 inches. The 
wheat was somewhat fired at the base and many of the younger tillers were 
dead and dry, as were also the two or three basal leaves on the larger tillers 
and parent plants. However, a part of this injury was the effect of frost. 
The stand, like that of the other cereals, was thin but fairly even, germination 
having occurred under rather favorable moisture conditions. On April 15, 
at the time of planting, more than 10 per cent of available moisture was 
found in the surface foot of soil (table 17). Although soil samples were not 
taken again until June 3, it seems clear from the rainfall records that mois- 
ture conditions were quite favorable, at least until the latter part of May. 
During the last half of April a total of 1.4 inches of rain fell at four well- 
distributed intervals, while from May 1 to 15, four other favorably distrib- 



Investigations at Burlington, Colorado. 



63 



uted rainy periods gave a total of 1.2 inches. In fact this, coupled with the 
high fertility of the soil (table 16), undoubtedly accounts for the very marked 
early growth and the abundance of tillers, both phenomena being detri- 
mental to the crops at a later period. 

Table 17.— Water-content in excess of hygroscopic coefficient in crop plats at Burlingto n, 1920. 



Dat 



April 15. . . 

June 3 

lime 12 . . . 
June 25 . . . 

July 2 

July 8 

July 20. . . 
August 5. . 
August 24 . 



Wilting coefficient 
Hygroscopic coefficient 



to 0.5 foot. 



22.0 
5.3 
0.4 
6.4 

-2.0 

-2.0 
0.5 
4.4 

-0.7 



13.3 
10.9 



0.5 to 1 foot. 



10.5 
6.4 
3.8 
1.7 
-1.1 
-0.4 
-2.6 
0.0 
-0.9 



13.3 
10.9 



1 to 2 feet. 



0.5 
3.1 
1.2 
0.8 
0.0 
-1.4 
-2.8 
1.3 
-2.2 



14.0 
12.2 



2 to 3 feet. 



0.1 
5.1 

2.7 



14.5 
12.0 



3 to 4 feet. 



-0.4 
-0.6 

1.6 

1.8 
2.0 
-1.9 
-1.8 



14.0 
11.4 



On June 3 a small margin of available water (3 to 5 per cent) still occurred 
in the first 3 feet of soil, but by June 12 a deficiency was indicated by the 
behavior of the plants. As a result of the drought (no ram m sufficient 
amount to wet the soil had fallen from June 1 to 12), many of the leaves 
were rolled and some did not recover their turgidity even during the night. 

Temperatures during the last half of April were low, falling below 32 F. on 
11 nights. The mean monthly temperatures for April and May were 41.2 
and 57.8° F. respectively. Frost occurred on May 15 and did some injury 
to the crops. Only 3 clear days occurred in April and 5 in May. During 
the last week of this interval the soil-temperature at a depth of 6 inches (in 
an adjacent area of grassland) averaged 65° F. while the air temperature 
gave an average of 80° F. during the day (maximum 100 F.) and 57 F. by 
night (minimum 43° F.). The evaporating power of the air was 47 c. c. per 
day 85 per cent of which normally occurs during the hours of daylight, 
the 'humidity often falling to 15 per cent or less. These aerial conditions, 
coupled with the low water-content of the soil, readily explain the semi- 
wilted condition of the crops. The soil in the plat where the wheat was 
excavated was underlaid at a depth of 2.7 feet with a rather poorly devel- 
oped, light-colored hardpan, which, like the more ashy loess beneath, was 

very dry. , - 

Root counts were made on a large number of plants. The number of 
roots varied from 15 to 19. Not infrequently 5 to 9 of the younger ones had 
grown an inch or two and died, apparently from drought. The extreme 
depth reached by several roots was 2.5 to 2.7 feet, although a single root was 
traced in the soil of an ancient rodent's burrow, where water had penetrated, 
to a depth of 3.3 feet. However, the working depth of the root system as a 
whole was only 1.3 feet. The plants had a wide lateral spread, and not in- 
frequently roots extended laterally for 10 or 12 inches in the surface 6 inches 
of soil. Others gave a maximum horizontal spread of 1.2 feet m the surface 
foot. The entire root system was much more profoundly branched than 



64 Development and Activities of Roots of Crop Plants. 



was that of wheat grown at Lincoln. The primary laterals varied in length 
from 0.3 to 3.0 inches, frequently as many as 20 to 27 branches occurring on 
a single inch. Secondary laterals, 0.2 to about 0.5 inch in length, were nu- 
merous. Even the root-ends were well-branched with rather long laterals 
(fig. 27). Thus the root system, although largely confined to the surface 
2 feet of soil, because of its wide lateral spread and profuse branching, was 
well adapted to extract water and solutes from these soils of low water- 
content. The roots in the surface 6 or 8 inches were not at all fleshy, but 
tough and wiry, and many were at this time drying out. 

A final examination of wheat was made on July 7, when the plants were 83 
days old. They had fully headed out by June 25, and were now in the dough 
stage. The crop averaged 1.7 feet in height, with a maximum height of 1.8 
feet. The plants were thin on the ground, and many had no tillers, while 




Fig. 27. — Wheat roots showing normal differences in branch- 
ing at Lincoln, L, and Burlington, B. 1, at 
depth of 1.5 feet; 2, root-ends. 



some showed 4 to 6 tillers, but the average total number of stalks in selected 
meter quadrats was only 201. Most of these did not head out (plate 2 a). 
When harvested on July 19, the heads were well filled and the grain was of 
fair quality. 

The interval since the last examination on June 12 was one of scant water- 
supply and high evaporation. Rain fell on 11 days, but only 4 showers of 
more than 0.2 inch occurred, heavy rains falling on June 18 (1.35 inches) 
and on July 5 (0.45 inch). A glance at the water-content of the soil given 
in table 17 is sufficient to show the prevailing drought. During the latter 
part of the period the crops ripened and dried rapidly. Three days after 
the 0.45-inch rain, on July 5, no water was available in the surface 2 feet of 
soil. Although samples for water-content determinations were taken as 
usual in duplicate, local differences in soil-structure caused rather noticeable 
differences in run-off and penetration in closely adjacent areas in the same 



Investigations at Burlington, Colorado. 



65 



level plat, so that a variation of 1 or 2 per cent of moisture was not uncommon. 
This variation probably accounts for the water-content apparently being 
exhausted below the hygroscopic coefficient. It seems, however, that crop 
plants growing in these more arid soils have a greater ability to more thor- 
oughly exhaust the water-supply than when grown in more humid regions. 
This is due possibly to the development of greater osmotic pressure, and cer- 
tainly to a more thorough occupancy of the soil area by roots. The latter 
establishes a closer relation to all available soil-moisture, an exceedingly 
important condition at a time when the soil becomes so dry that all capillary 
movement of water ceases. 

The soil-temperatures during the period were high. The average daily 
temperature ranged from 65° (minimum 57°) to 76° F. (maximum 85 F, 
fig. 28). The average daily temperatures of the surface 6 inches of soil were 

August 



June 



July 



so 



70 



60 



50 



























s \ 




















/-I 

/ 

/ 

/ 


s \ 
s \ 











































Fig. 28— Average day and average night air-temperatures and average 
daily soil-temperature (broken line), Burlington, 1920. 

4° to 7° F. higher after the first week of July than those at Lincoln. This was 
undoubtedly due to the drier and more insolated soil, for at Lincoln both day 
and night temperatures of the air averaged higher than those at Burlington. 
At Burlington the air-temperature ranged from 67° to 84° F. by day (maxi- 
mum 99° F.) and 51° to 60° F. (minimum 43° F.) by night. Soil-tempera- 
tures at depths of 1 to 4 feet were about the same at both stations. Owing 
to the lag of soil-temperature (at 6 inches depth) at all stations, both m reach- 
ing a maximum (about 6 p. m.) and a minimum (about 7 a. m.), the day and 
night averages at any station were very nearly the same. The great range of 
air-temperatures from day to night (usually 35° to 45° F.) is significant, for 
high daily temperatures coupled with low humidity accentuate drought con- 
ditions, causing partial wilting and cessation of photosynthesis and growth. 
However, at night conditions are reversed and plants usually have oppor- 
tunity to readjust their water-equilibrium. In fact, the average nightly 
humidity (79 to 90 per cent), which is caused largely by the low temperature, 
was greater than that at Lincoln. However, the average daily air-moisture 
(39 to 53 per cent) was much less (fig. 29). Not infrequently the hygro- 
graph registered as low as 17 to 25 per cent. 

It should be pointed out that the season of 1920 was one unusually favor- 
able for crop development. On several occasions fogs were noted which did 
not clear away until the middle of the forenoon. Such atmospheric con- 



66 



Development and Activities of Roots of Crop Plants. 



ditions are very favorable for the conservation of water by plants. During 
these periods the wind, an important ecological factor, was still or of low 
velocity. Normally it is quite pronounced, averaging 130 to 160 miles per 
day and two to four or more times this amount during very windy weather. 
It plays an important part in desiccating both plants and soil. Throughout 
the period the evaporating power of the air ranged from 23 to 39 c. c. daily 
(table 18). Owing to the cool nights, which cause a rise in humidity, coupled 



70 



50 



40 



June July 
2 3 4 1 2 



August 

4 12 3 4 







\ 

\ 

\ 

N 

■' 








\ 
\ 








/ 

/ 

/.. 














'"V - 
\ 
\ 

\ 

~~~ i 






\ 

\ 


/ 












^ 










— ^ 










\ \ 




/ 

i 

l 








' i 


\X 

— V— 


i 
/ 

/ 

_v — 






^ > 
\ 

\ 

\ 

\ 




i 

t 

i 

/ 
/ 






\ 

\ 

\ 

\ 

V 


/ 

t 

I 

I 

I 


\ 

> 


/ 

t 

t 










' ' 








t 





Fig. 29. — Average day humidity (lower lines) and average night humidity 
(upper lines) at Lincoln (solid lines) and Burlington 
(broken lines), 1920. 

with the lesser wind movement, the evaporating power of the air is low. For 
example, from June 28 to 30, 1921, with typical clear, hot days and cool nights, 
the average day evaporation (6 a. m. to 6 p. m.) was 48 c. c. with 104 miles of 
wind, while the average night evaporation was only 10 c. c. with 51 miles of 
wind. Thus 83 per cent of the evaporation occurred during the day period. 
The conditions of low available water, high soil and air temperatures, es- 

Table 18. — Average daily evaporation at Burlington, 1920. 



June 3 to 11 46.9 

June 11 to 18 34.8 

June 18 to 25 22.4 

June 25 to July 2 38.4 

July 2 to 8 38.6 

July 8 to 15 42.1 



July 15 to 20 31.8 

July 20 to 27 44.2 

July 27 to Aug. 5 26.0 

Aug. 5 to 15 24.2 

Aug. 15 to 18 59.8 

Aug. 18 to 25 22.6 



pecially by day, combined with great wind movements and low humidity, 
caused not only a dwarfing of the above-ground plant parts, but resulted 
in an extensive development of the root systems. 

The wheat roots were very abundant to the depth of the hardpan, 2.7 
feet. This dry layer determined the maximum penetration, which had 
not increased since the last examination, although the working depth was 
now only a little less than the maximum. Likewise, the lateral spread had 



Investigations at Burlington, Colorado. 



67 



increased but slightly. Although the soil was very hard and dry and was 
removed with exceedingly great difficulty, it could be plainly seen that the 
wonderfully developed roots thoroughly occupied every cubic inch where 
available water was present. 

Oats, Avena sativa. 
Oats were also examined on June 12. The crop had an average height of 
10 inches, although some plants were 13 inches tall. The tillering was not 
heavy; 2 or 3 tillers was an average number, while very rarely more than 5 
occurred. Young tillers were infrequent. While the crop was in fairly 




Fig. 30.— Oats at maturity, Burlington, 1921. 



good condition, many plants were somewhat fired at the base. Some of the 
older leaf-tips showed effects of frost injury. As a result of the drought 
the leaves were more or less rolled, but scarcely to the extent of those of wheat 
or barley, some of which did not become turgid at night. 

Some of the longest roots extended to a depth of 2.4 feet where very 
dry soil occurred. The working depth was the same as for wheat, 1.3 feet. 
The root habit, as regards surface lateral spread, abundance of roots at all 
angles to the vertical, and profound branching to the very root-ends, was 
very similar to that of wheat, but of slightly less degree m every respect. 



68 Development and Activities of Roots of Crop Plants. 

This may have been due in part to the smaller number of plants supported 
by the oat roots. Compared with growth in more humid regions, the roots, 
while less extensive, were much more profoundly branched. Many young 
roots which had originated near the surface and were densely woolly with 
root-hairs, had dried out and died after reaching a length of only 0.3 to 3 
inches. This fact leads one to believe that the excellent development 
of long, rebranched laterals, especially in the surface 1.5 feet of soil, may be 
correlated not only with the prevailing relatively low water-content, but 
also with the lack of ability on the part of the plant to produce new absorbing 
organs in the dry surface-soils. 

On July 7, when the oats had reached a height of 1.5 feet (maximum 1.8 
feet) and were in the dough stage, roots were again examined. The crop 
had been somewhat damaged by grasshoppers, but the grain was well filled 
and of good quality when harvested July 19. In making the excavation 
preliminary to root study, a very dry hardpan was encountered at a depth 
of 2.7 feet. It had a thickness of about 1.3 feet. Below this stratum the 
soil was mellow and powdery. Roots were quite abundant to the hardpan 
layer, and the working depth reached approximately this level. As in the 
case of wheat, the surface soil was also completely filled with exceedingly well 
branched roots, these apparently being a response to available water-content 
furnished by summer showers. The lateral spread of roots was about 10 
to 11 inches. This root habit is markedly different from that of plants 
grown from the same seed in more moist soil and in a less arid climate (cf. 
figs. 21 a and 30). 

Barley, Hordeum vulgare. 

Barley was examined also on June 12. The plants were about 11 inches in 
height, the tallest exceeding this by only 2 inches. The number of tillers 
varied from 2 to 6 and averaged 3 or 4 per plant. 

The working depth of the barley roots was determined at 2 feet; a few 
penetrated 4 to 6 inches deeper. The general root habit was very similar 
to that of wheat, the lateral spread being slightly less. In the surface 6 
inches of soil the primary branches were 2 to 3 inches long, the secondary 
ones 0.3 to 0.5 inch, and all were densely hairy. On one root, at a depth of 
4 inches, 58 primary laterals were counted on a segment of root only 2 inches 
long. These had an average length of about 1 inch and were fairly well 
supplied with secondary branchlets. On another root, at a depth of 5 inches, 
26 branches occurred on a segment an inch in length. These cases well 
illustrate the profound root development in the first foot of soil. As already 
described for wheat and oats, numerous young roots from 0.3 to 3 inches long 
had died. These superficial roots must have had their origin during a time 
when moist soil prevailed; they were densely covered with root-hairs. As 
a whole, barley roots, like those of oats, are scarcely as well-developed as are 
those of wheat. 

By June 25 the barley was nearly all headed out. The crop was somewhat 
damaged by grasshoppers. On July 7, when the root system was again 
studied, it was in the dough stage. The plants averaged 1.7 feet in height, 
with a maximum height of 2 feet. An average of 254 stalks were counted 
in selected square meters. The tillers averaged only one per plant, many 
having dried out and died. The roots extended even more widely in the 



Investigations at Burlington, Colorado. 



surface foot than those of wheat. Great mats of branches occurred in the 
surface 6 to 12 inches of soil, forming a profoundly developed absorbing 
system on all sides of the plant, even to a distance of 1 to 1.2 feet. The 
working depth was about 2.5 feet, while some roots reached a maximum 
of 2.9 feet, where they encountered the very dry hardpan. 

Alfalfa, Medicago sativa. 
Alfalfa was sowed at Burlington at the same time as the cereals already 
described, on April 15. On June 11, when the roots were examined, the 
plants were about 4.5 inches high, although the tallest ones reached 6 inches. 
The stand was quite good, and the plants had a normal green color, but some 
wilted badly during the hottest part of the day. Hardpan occurred m this 
plat at 2.2 feet depth. While the surface 6 inches of soil was very dry, below 
this a small amount of available water occurred to the hardpan layer (table 
17). Most of the roots were about 1.7 feet deep, although some were traced 




Fig. 31.— Alfalfa excavated at Burlington, June 28, 1921, during the second year 

of growth. 

to 2 3 feet. The root habit, especially in the surface soil, was quite like that 
described at Lincoln, but in the deeper layers the roots were found to be more 
abundantly branched. Moreover, the branches were longer and extended 
nearer the root-ends. . , , K 

A second examination was made on July 7, when the crop was about 5 
inches high. Considerable variation in the development of the plants was 
noticeable, however, many being much smaller than the average and a few 
8 inches tall. The trench was only a few feet from the preceding and the 
hardpan occurred at 2.1 to 2.3 feet depth. The soil, and especially the 
surface 8 inches, was very dry. Roots were abundant to the hardpan layer, 
but none extended beyond. They were characterized by a much more 
profuse branching than was found at Lincoln, and the lateral spread was 
also much greater. Undoubtedly this root habit is an adaptation to secure 



70 Development and Activities of Roots of Crop Plants. 

the necessary supply of water, which occurred in limited amounts and was 
confined here to the surface 2 or 2.3 feet of soil. Chemical analyses (table 
16) show that the soil is rich in all the necessary nutrients. Nodules occurred 
on the roots at all levels. Aeration could not have been a limiting factor to 
growth in this dry soil, and undoubtedly water played the dominant r61e. 
This conclusion is substantiated by further studies. 

A final examination was made on August 25. The water-content (table 17) 
was rather uniformly low; however, determinations were made only at lather 
long intervals. Showers of 0.86 inch occurred July 16 and 17; 1.26 inches of 
rain fell on July 26; and 1.34 inches early in August; while a drought period 
of 15 days' duration was broken by 0.72 inch of rainfall on August 20. 
Although the crop was often in a semiwilted or wilted condition during the 
periods of stress (figs. 28 and 29 and table 18), when more favorable conditions 
occurred growth was resumed. Thus, by August 25 the plants had increased 
6 inches in height since July 7, the tallest reaching 11 inches. They had 
blossomed and most of the flowers had dried. 

In the new trench, which was not far from the former ones, the haidpan 
came to within 2 feet of the surface. This layey delimited the depth of root 
penetration and none was found deeper. The tap-roots were 3 or 4 mm. or 
less in diameter. They were profusely branched with both large and small 
laterals. Not infrequently some of the laterals were equal in size to the tap. 
Many spread at various depths almost parallel with the soil surface or obliqued 
downward, reaching distances of 1 to 1.5 feet, horizontally from the tap. 
Some were found with a maximum lateral spread of 1.5 to 2 feet. Small 
branches were numerous. The soil was remarkably well occupied by the 
network of roots, a condition quite unusual in fields of young alfalfa of more 
humid regions (c/. figs. 25 a and 31). 

Sweet Clover, Melilotus alba. 

The first examination of the root development of sweet clover was made 
on June 11, when the plants were 57 days old. They averaged 3 inches 
in height, although some were an inch taller. The stand was quite good. 
The tops were beginning to branch and the crop was in fairly good condi- 
tion, except, as a result of drought, many of the leaves on some plants were 
partly wilted and folded during the hotter portion of the day. Not a few 
of the roots reached a maximum depth of 2.3 feet, and one, following the 
course of a large decayed Sudan-grass root, penetrated a foot deeper. The 
working depth was about 2.0 feet. The roots were mostly much smaller in 
diameter, especially in the dry surface 6 inches of soil, than those at Lincoln, 
but the root development as regards number, branching, and lateral spread 
was almost identical with the latter. In the deeper soil, however, branching 
was much better developed. Considerable variation occurred in regard to 
abundance of laterals near the tip. On some plants as many as 15 branches 
about 0.2 inch long occurred on a single inch of tap-root, while on others they 
were scarce. Numerous counts as regards number of primary and secondary 
branches showed that they were not only more abundant, but also averaged 
longer than those in the more humid soil eastward. 

By July 7 the crop had reached a height of about 5 inches, although some 
especially well-developed plants were 8 inches tall. The more thrifty appear- 



Investigations at Burlington, Colorado. 



71 



ance of the crop when compared with the plat of alfalfa was undoubtedly 
due in part to the greater depth of moist soil. In the portion of the sweet- 
clover field examined, the hardpan was 6 to 8 inches deeper than in the portion 
of the alfalfa field where roots were excavated. Except for rare cases of 
roots entering burrows, etc., none extended to depths greater than 2.8 feet, 
where hard, dry soil occurred. However, most of the roots reached this 
depth. As with alfalfa, they were furnished both with more numerous and 
longer laterals than were those at Lincoln. In the first foot of soil the laterals 
were often more superficial in position, a response no doubt due to the stim- 
ulus of moisture in the superficial layers and its dearth at lower levels. The 
tap-root branched profusely throughout its length almost to its very tip. 
Tubercles were abundant, often occurring in large clusters. 

On August 25, when a final exmination was made, a long trench was dug 
in such a manner that while one end extended in heretofore undisturbed soil, 
the other reached into the territory of the former trench. As usual, the old 
trench had been sunk a foot or two below the deepest roots, and this one 
had been deepened still further (to about 6 feet) in order to examine the sub- 
soil. It had been refilled with the mixed soil and subsoil. A marked dif- 
ference in growth and vigor of the plants growing adjacent to the old trench 
and those in the undisturbed area was noted. While those in the latter area 
were only about 1 foot tall, the others were 1.3 feet high, more branched, and 
of better color. Where the dry, hardpan layer occurred at 2.7 feet depth, root 
penetration was limited to the soil above this layer. In general, the root habit 
was very similar to that of the alfalfa already described, the number of 
branches, their greater lateral extent and degree of rebranching being quite 
unlike plants from the same lot of seed grown in the moist soil at Lincoln. 
However, the plants growing at the sides of the old trench had extended their 
roots into the loose soil, which had been fairly well moistened, due to heavy 
rains, and, undoubtedly, to the entrance of run-off water from the surrounding 
area. Here a few roots were traced to depths of 6.8 feet, while many extended 
into the fifth and sixth foot of soil. In this new soil area the root develop- 
ment was similar to that described for plants at Lincoln. 

Summary of Crop Development. 
Crops grown at Burlington, Colorado, were, owing to the unfavorable 
climatic conditions, thin of stand, and the above-ground parts much dwarfed. 
Oats when mature averaged only 1.5, and wheat and barley 1.7 feet in height 
respectively. Root-depth was limited by water penetration and did not 
exceed 2.9 feet. Alfalfa and sweet clover, when 132 days old on August 
25, were only a foot high and rooted entirely in the surface 2 to 2.7 feet of 
son. Early spring environment, except for the low temperatures (especially 
at night), was quite favorable to crop growth. The cereals tillered freely 
and because of the rich soil all the crops grew quite too luxuriantly to suc- 
cessfully endure the drought conditions of June and later summer. Because 
of low water-content of both air and soil, all of the crops were from time 
to time in a semiwilted condition. Many tillers from the cereals died, as did 
also new roots put forth during intervals when the surface soil was moist. 
The extraordinary development of long, widely spreading, and profusely 
branching laterals, which thoroughly filled the soil above the hardpan layer 



72 



Development and Activities of Roots of Crop Plants. 



(at 2 to 2.7 feet), gave the plants a root development quite out of proportion 
to the tops and markedly different from those of more moist soil. This root 
development agrees with earlier studies of cereal crops, including winter- 
grown varieties, and in many respects with that of the native vegetation of 
the short-grass plains (c/. Weaver, 1920). 

Summary of Environment and Crop Development at All 

Stations, 1920. 

The stations at Lincoln, in southeastern Nebraska, Phillipsburg, in north- 
central Kansas, and Burlington, in eastern Colorado, are at altitudes of 1,100, 
1,935, and 4,160 feet respectively. The vegetational expression of the 
climate at the three stations respectively are true-prairie, mixed-prairie, 
and short-grass plains. The precipitation for the growing-season, which 
begins 2 to 4 weeks later at the higher elevation, is shown for each station 
in figure 32, where the mean precipitation is also included. An examina- 




Fiq. 32. — Mean precipitation in inches (black) and precipitation for 1920 at Lincoln (left), 

Phillipsburg, and Burlington. 



tion of this figure shows that the rainfall at all stations during March was far 
below normal, but approximately twice normal during April, when the crops 
were planted. Aside from a deficiency of nearly half the normal rainfall 
at Lincoln and Phillipsburg during June, and an increase to twice the normal 
at the latter station during August, no marked irregularities in the pre- 
cipitation occurred. The total precipitation at Lincoln during the period 
was 18.8 inches, which was only 0.3 inch greater than that of Phillipsburg. 
The precipitation at Burlington was about 75 per cent as great, but owing to 
numerous light showers and great run-off during heavy ones, its actual effi- 
ciency in increasing water-content of the soil was probably only half as great 
as the number indicates. 

The soil at the Lincoln station consists of a fine-textured silt loam under- 
laid with clay loess. At Phillipsburg the mellow silt loam gives way at a 
depth of about 1 foot to a very mellow loess subsoil. The very compact silt 



Investigations at Burlington, Colorado. 



73 



loam at Burlington is underlaid at about 2.5 feet with hardpan, while powdery 
loess occurs below this level. All of the soils are very fertile, their physical 
effect upon the water-content affecting crop production to a far greater degree 
than their chemical composition. 



June July August 

2 3 4 1 2 3 4 12' 















/ 

/ 


t 
\ 


















y 


/ 

/ 

/ 

\ 

— V 


\ 

N 

\ 

\ 

\ 








l_l 


n 




b 


\ 


/ 








l\ 




// 
// 

I: 




V 

/ 


















U 

/ 























Fia. 33. — Average daily soil-temperature at Lincoln (solid line), Phil- 
lipsburg (long broken lines), and Burlington (short broken 
lines), 1920. 



June July August 

3 4 1 2 3 4 1 2 2 




55 • 1 » 1 1 1 1 u 1 1 

Yiq. 34. — Average daily air-temperature at Lincoln (solid line), Phil- 
lipsburg (long broken lines), and Burlington (short broken 
lines), 1920. 

A study of the water-content to a depth of 4 feet shows that at both the 
upland and lowland stations at Lincoln at least 7 per cent (and usually 10 
to 20 per cent) available watei was present at all depths below 6 inches until 
the middle of July. At no time during the growing-season was the supply 
of available water, even in the surface 6 inches, entirely exhausted, a margin 
of 4 to 9 per cent being maintained in the deeper soil even during the driest 
part of the season. At Phillipsbuig the water relations were less favorable. 



74 



Development and Activities of Roots of Crop Plants. 



On July 1 no water was available in the surface 6 inches of soil, a week later 
only 1 or 2 per cent was available from 1 to 3 feet, while by the latter part of 
the month a deficit occurred to 2 feet and less than 1 per cent was available 
to 4 feet. Somewhat similar conditions prevailed late in August. Water 
relations at Burlington were even less favorable for plant growth than those 



TMR50AY FRIDAY. SATURDAY. SUNDAY. 




Fig. 35. — Hygrothermograph records from Lincoln (upper) and Burlington, June, 1921; 
light lines temperature, heavy lines humidity. 



at Phillipsburg. While the surface foot was well moist during April, May, 
and early in June, only a small available supply (0 to 5 per cent) occurred in 
the second and third foot, while at no time during the season was the soil 
moist below the hardpan layer (about 2.7 feet deep). An available supply 
of only 1 to 6 per cent was found at all levels above the hardpan throughout 



Investigations at Burlington, Colorado. 



75 



June, while during the remainder of the season a deficiency at all levels was 
not uncommon. 

Soil temperatures at a depth of 6 inches were highest at Lincoln (70° to 
77° F.), and lowest at Burlington (64° to 72° F.) during the first half of June, 
but by the last week in June this relation was reversed, the soil at Burlington 
remaining warmest throughout the season. The average weekly differences 
were often 6° to 8° F., the Lincoln soil being coldest, that at Phillipsburg 
intermediate, while the dry soils at Burlington had the highest temperature 
(fig. 33). 

The average daily air-temperature throughout the season was usually 
5° to 7° F. colder at Burlington than at Phillipsburg, while that at Lincoln was 
generally higher than that at Phillispburg (fig. 34). 

The average day humidity at Lincoln ranged between 49 and 65 per cent 
and was usually higher than that at Burlington. However, the average night 
humidity at Lincoln (67 to 82 per cent) was usually exceeded by that at 

June July August 

2 3 4 1^ 3 412 3 4 




L. J 1 I 1 ' 1 1 1 ' 1 ' 

Fig. 36. — Average daily evaporation at Lincoln (solid line), Phillips- 
burg (long broken lines), and Burlington (short broken 
lines), 1920. 

Burlington by about 8 per cent until late in July (fig. 29). Conditions at 
Phillipsburg were intermediate. The much greater daily range of both 
temperature and humidity at the Burlington station when compared with 
that at Lincoln is shown in figure 35. This combination of high temperature 
and low humidity, which occurs rather regularly in the afternoons at Bur- 
lington, when coupled with dry soil, are conditions very unfavorable for plant- 
growth. 

Wind movement is much greater at Burlington than at either of the other 
stations and is an important factor in desiccating both crops and soil. An 
average day velocity of 8 or 10 miles per hour (at a height of 0.5 meter) is 
quite usual, while periods lasting for several days when the velocity reaches 
20 or 30 miles per hour are not uncommon. The amount of wind is less at 
PhiUipsburg and much less at Lincoln (for example, 4 miles per hour average 
daily from July 13 to September 19, 1916 (c/. Weaver, 1919 : 23). 



76 



Development and Activities of Roots of Crop Plants. 



The evaporating power of the air, which integrates, to a certain degree, 
the factors of radiant energy, humidity, and wind movement, was greatest 
throughout the season (23 to 60 c. c. average daily evaporation) at Burlington, 
intermediate at Phillipsburg (11 to 32 c. a), and least (9 to 25 c. c. at Lincoln 
(fig. 36). 

Thus the conditions for crop-growth as regards rainfall, water-content of 
soil, temperature, humidity, wind, and evaporation were most favorable 
at Lincoln, intermediate at Phillipsburg, and least favorable at Burlington. 
These conditions are indicated by the native vegetation and borne out by the 
growth of crops. 

The relative height of the mature oats and barley at the several stations 
is shown in plate 3 (cf. also, plate 2 b, for wheat). These plates also show 
the comparative yield from an average square meter; the bundle on the right 
was taken in every case from the lowland plats at Lincoln. In table 19 may 



Table 19. — Summary of cereal crop development, 1920. 



Crop and station. 


Date of 
harvest. 


Ave. 
height. 


Ave. yield 
in grams 
per sq. m. 


Weight 
of 1000 
kernels. 


Working 
depth. 


Max. 
depth. 


Max. 
lateral 
spread. 


Oats: 




feet. 




grama. 


feet. 


feet. 


feet. 


Lincoln 


July 12 


3.0 


706 


20.1 


2.8 


4.8 


0.8 


Phillipsburg 


July 20 


2.6 


379 


16.6 


3.3 


6.0 


0.8 


Burlington 


July 19 


1.5 


175 


16.2 


2.7 


2.7 


0.9 


Wheat: 
















Lincoln 


July 15 


3.2 


740 


29.8 


3.5 


4.8 


1.0 


Phillipsburg 


July 20 


2.3 


322 


9.1 


3.0 


5.8 


1.0 


Burlington 


July 19 


1.7 


205 


20.1 


2.7 


2.7 


1.2 


Barley: 
















Lincoln 


July 12 


2.7 


607 


32.7 


3.3 


5.4 


1.0 


Phillipsburg 


July 17 


2.4 


407 


14.7 


3.3 


6.7 


1.0 


Burlington 


July 19 


1.7 


176 


23.9 


2.5 


2.9 


1.2 



be found a summary of the height, yield, and root development of the cereals 
at the several stations. The yield is the average of 25 to 30 square-meter 
quadrats taken from the several plats at the three stations respectively, 
that from Lincoln being from the lower crop area. All of the crops were 
assembled in the botanical laboratories of the University of Nebraska and 
thoroughly air-dried before weighing. A study of the table shows that the 
crops are progressively shorter from Lincoln westward and that the average 
yield is also less. The results correlate well with those obtained during 1919, 
when data from a large number of fields in the different grassland associa- 
tions were obtained (Weaver, 1920 : 123). 

Regarding weight of threshed grain, Lincoln is highest in every case, and 
Burlington second except in the case of oats. The low yield at Phillips- 
burg was due in part to the rust epidemic. 

Root development, as regards both working depth and maximum extent, 
is greatest in every case (except one) at Phillipsburg, although these depths 
average less than those found at Peru during 1919. The shortest roots 
occurred at Burlington, where the hardpan demarked at once the limit of 
water penetration and root extent. The greater root extent at Phillipsburg 



Investigations at Burlington, Colorado. 



77 



than at most mixed-prairie stations (Weaver, 1920 : 122) is in agreement with 
results obtained the preceding year and is probably due to the unusually 
moist subsoil resulting from 11 inches of excess precipitation during 1919, 
coupled with rather arid above-ground environment during the growth of 
the crops. In general, the root habit of the cereals was very similar at Phil- 
lipsburg and Lincoln, but markedly different from those at Burlington, where 
the abundance of roots, branching, etc., was much more pronounced in the 
surface soils 

During July, and again in August, 400 alfalfa plants of average size were 
carefully selected at each of the stations, cut just below the crown, thoroughly 
air-dried in the laboratories in Lincoln, and the dry weight obtained. Similar 
collections of sweet clover were made, each one containing 300 plants (plate 4). 
The development of the leguminous crops is summarized in table 20, where 

Table 20. — Development of leguminous crops, 1920. 



Crop and station. 



Alfalfa: 

Lincoln 

Phillipsburg . 

Burlington. . 
Sweet clover: 

Lincoln 

Phillipsbui g . 

Burlington. . 
Alfalfa: 

Lincoln. 

Phillipsburg . 

Burlington. . 
Sweet clover: 

Lincoln. . . . 

Phillipsburg 

Burlington. 



Date of 
cutting. 



July 12 
July 9 
July 8 

July 12 
July 9 
July 8 

Aug. 9 
Aug. 4 
-Aug. 5 

Aug. 9 
Aug. 4 
Aug. 5 



Ave. 
height. 



feet. 
1.5 
0.7 
0.4 

2.0 
1.3 
0.4 

1.8 
1.2 
0.6 

2.5 
1.7 
0.8 



Dry weight of 
400 av. plants. 



grams. 
528 
292 
122 

2840 
461 
213 

739 
601 
214 

n,103 
869 
323 



Max. 
depth. 



feet. 
5.7 
5.0 

i2.3 

5.5 
5.7 
2.8 

5.9 

i2.0 



2.7 



Date of 
excavation. 



July 24 
July 10 
July 7 

July 24 
July 9 
July 7 

Aug. 10 

Aug. 25 



Aug. 25 



1 Depth determined by hardpan. 

2 At each station 300 sweet clover plants were taken. 

the data for Lincoln are from the lower crop plats. A study of the table 
shows that both the height-growth and dry weight, like that of the cereals, 
correlates directly with available water-content, being greatest at Lincoln 
and least at Burlington. Root penetration is greater for sweet clover at 
Phillipsburg, but less for Alfalfa than at Lincoln, while at Burlington the 
depth of penetration of both is only about half as great. Tap-roots with 
relatively few short branches characterized the root system at the two less 
arid stations, but at Burlington the abundance of large, profusely branched 
laterals above the hardpan was very pronounced. 



78 Development and Activities of Roots of Crop Plants. 

V, INVESTIGATIONS AT ALL STATIONS IN 1921. 

In order to further check the results on root development, crops were 
again grown at all the stations during 1921. These consisted of University 
No. 21 oats, Marquis Spring wheat, and Manchuria barley. At the Peru 
station, Early Ohio potatoes and Iowa Silver Mine corn were also grown. 

The small cereals were planted in plats of 25 square meters each and at 
the same rate (which was somewhat greater than the preceding years, p. 41) 
at all stations, viz, oats 64, wheat 90, and barley 72 pounds per acre. The 
seed was from the same lot and the time of planting at the several stations 
was approximately the same (March 24 to 30). 

Investigations at Peku, Nebraska. 

The experimental plats at Peru were the same as those of the preceding 
year, the small cereals being planted on the land formerly occupied by corn. 
A good seed-bed was prepared, the seed sowed evenly, hoed in, and the 
plats leveled off with a rake. The plat for potatoes was prepared by spading 
the soil to a depth of 8 inches. The tubers, from which all but one bud had 
been excised, were planted in rows which were 3 feet apart. The pieces 
of tubers were placed 2 feet apart in the row and at a depth of 4 inches. 
The corn was level-planted on May 17 at a depth of 3.5 inches after the 
plat had been spaded to a depth of 6 inches. The rows were 3 feet apart and 
the kernels were placed at intervals of 1.3 feet in the row. Both corn and 
potatoes were tilled with a hoe in such a manner as not to disturb the roots. 

Owing to a deficiency in rainfall, coupled with poor distribution, the crops 
did not develop normally. At the time of harvest, about June 30, the oats 
averaged 2.4 feet in height; the crop, though evenly developed, was thin, 
having tillered so poorly that many single stalks occurred, while many others 
had but one or two tillers. However, the grain was well filled. The stand 
of barley was even thinner, single stalks being numerous and few plants having 
the usual numbers of tillers. Barley averaged 2.4 feet in height and had 
well-filled heads. Wheat was the poorest. The crop was very thin and 
uneven in development; more single stalks occurred than those with tillers. 
It varied in height from 1.6 to 2.8 feet, with an average of about 2 feet. 
The heads were small and only partly filled. Compared with 1919, also 
a drought year, oats and wheat were 7 or 8 inches shorter in average height, 
but the barley slightly taller. The stand was thinner in every case. 

An examination of the rainfall and soil-moisture records makes clear the 
degree of drought. The rainfall during April was only 1.79 inches, over 
70 per cent of which fell at one period (April 13 to 16). The rainfall for 
May, 3.07 inches, was 1.56 inches below normal and also poorly distributed, 72 
per cent falling on May 7 to 10. June, 1 with 3.35 inches of precipitation, 
practically all of which occurred befoie the middle of the month, had a 
deficiency of 1.38 inches. 

The available water-content of the soil in the oat plat and also in a check 
plat of similar size kept free from all vegetation, is given in table 21. The 
relatively low water-content at the time of planting, and especially during 
June, is quite unusual for this station (cf. fig. 12). Table 21 indicates that 



1 Record from rain-gage installed at Peru; other records from Nebraska City. 



Investigations at All Stations. 



79 



by April 25 root activity was confined largely to the first foot or two of soil, 
while on June 10 the oats plat was much drier to 4 feet than the control. It 
should be stated in this connection that the potatoes did not exhaust the 



Table 21. — Water-content in excess of hygroscopic coefficient, Peru, 1921. 





Depth in feet. 


to 0.5 


0.5 to 1 


1 to 2 


2 to 3 


3 to 4 


Mar. 25, control 


7.2 


10.3 


10.9 


5.5 






9.5 


14.3 


14.9 


9.4 






15.2 


17.3 


15.0 


11.7 






13.6 


16.4 


16.2 


11.3 






10.7 


16.3 


15.6 


10.5 


'4^7 


May 10, oats 


22.5 


21.3 


19.9 


15.0 




May 21, oats 


6.6 


12.4 


14.2 


12.4 


ii!7 




10.7 


12.7 


12.9 


11.9 


10.0 




5.7 


4.3 


5.6 


6.3 


4.7 




0.5 


2.1 


3.0 


3.0 


3.5 


Hygroscopic coefficient. . . . 


8.9 


9.1 


8.9 


8.8 


9.2 



soil-moisture in any degree comparable with that of the oats. The potato 
plats on June 25 had 2.5 to 10 per cent more available water-content than 
the oats. 

The temperatures under which root growth occurred are given in table 22. 



Table 22. — Soil-temperatures at Peru, 1921. 



Date. 


0.3 foot. 


0.5 foot. 


1 foot. 


2 feet. 


3 feet. 


4 feet. 




°C. 


C. 


C. 


° C. 


C. 


°C. 


Apr. 12 ... . 


20.5 


16.0 


15.0 


13.0 


12.5 




Apr. 25 


17.0 


16.5 


15.5 


13.5 


12.0 




Apr. 30 


11.0 


12.5 


13.0 


12.5 


11.5 


10.5 


May 10 


20.0 


16.5 


15.0 


14.0 


13.5 




May 21 ... . 


28.5 


22.5 


20.0 


18.0 


15.5 


14.0 


June 10 


29.5 


25.5 


23.0 


21.0 


19.6 


18.0 



The relative root development of the mature crops during 1921 is compared 
with that of 1919 in table 23. 

From table 23 it may be seen that the oat roots penetrated more deeply 
than in 1919, which is the only exception to the smaller cereal crops being 
somewhat less deeply seated in 1921. These differences are probably due 
in part to the direct effect of soil-moisture upon root development, the 
deeper soils being less moist than during 1919, while the maximum amount 
of water occurred at 1 to 3 feet. It seems probable, also, that there is some 
correlation between the development of the above-ground parts, which were 
poorer during 1921, and root extent. It has been pointed out that the oats 
made the best aerial growth of all the smaller cereals. The only differences 
in general root habit of these cereals from those grown in 1919 were a less 
marked development of the roots into a superficial and a deeply penetrating 
portion and the fact that root-hairs were much more abundant on the root- 
ends in the drier soils of 1921. 



80 Development and Activities of Roots of Crop Plants. 

The potatoes examined had 53 and 60 roots respectively. The horizontal 
spread of the roots in the earlier stages of growth was very marked. The 
tendency of these roots to turn rather vertically downward at a later period 
was not so great during 1921 j perhaps not more than 30 per cent of the roots 
penetrated far beyond the 1.5 to 2 foot level. At the time of examination 
(June 25) the soil-level with the maximum water-content occurred at 1 to 
2 feet, the soil being drier both above and below this depth. This may 
account for the root behavior. The root-ends were much more branched 
than in 1919. In all other respects the root habit of potatoes was similar 
to that described (cf. fig. 11). 



Table 23. — Relative development of crops at Peru, 
1919 and 1921. 



Crop and 


Av. 


Working 


Maximum 


year. 


height. 


depth. 


depth. 


Oats: 


feet. 


feet. 


feet. 


1919 


3.0 


4.2 


6.7 


1921 


2.4 


4.5 


8.0 


Barley : 








1919 


2.3 


4.0 


6.3 


1921 


2.4 


4.0 


6.1 


Wheat: 








1919 


2.7 


4.3 


6.7 


1921 


2.0 


4.0 


6.6 


Potatoes : 








1919 


2.3 


3.2 


4.7 


1921 


2.0 


2.8 


4.3 


Corn: 








1919 


8.5 


6.0 


8.2 


1921 


8.5 


6.2 


8.3 



The corn, although excavated on August 8, 83 days after planting, had 
reached practically the same extent as regards both height and root develop- 
ment as that excavated on September 2, 1919. In fact, the lateral spread 
of roots was 8 inches greater (4.7 feet) than in 1919. However, the last 
6 or 8 inches of root-tips were still white and unbranched, indicating incom- 
plete growth. The shallower roots were even more profoundly branched, 
with 18 to 20 laterals per inch, than those which penetrated deeper. In 
every way the root habit agreed with that described for 1919 (cf. fig. 9)» 

Investigations at Lincoln, Phillipsburg, and Burlington. 

The experimental plats at Lincoln during 1921 were on a level area of 
soil, the physical and chemical nature of which was almost identical with 
that of the lowland plats (cf. p. 40). Potatoes had been grown on the area 
the preceding year. A good seed-bed was formed by plowing and harrowing 
a few days before hoeing in the crops on March 24. 

At Phillipsburg the crops were grown only a few meters from the 1920 
plats; the preceding crop was barley. The soil was plowed about 5 inches 
deep and harrowed on March 24 and the crops hoed in the next day. 

The crop plats at Burlington also adjoined those where roots had been 
dug the preceding year. The wheat and oats stubble had been plowed 



Investigations at All Stations. 



81 



about 6 inches deep early in November and a good seed-bed formed by 
repeated harrowing on March 30, just preceding hoeing in the crops. At 
this time, general farming operations had begun. 

The soil at all the stations was in good tilth as regards soil-moisture at 
the time of seeding. Owing to a late spring, with severe freezes and snow, 
especially during the first half of April, the crops developed rather slowly, 
particularly those at the stations with the higher altitudes. The com- 
parative development of the crops at the several stations on April 28 to 30 
is shown in table 24. The precipitation during this period was 3.2 inches 



Table 24— Crop development at the several stations, April 28 to 30, 1921. 



Crop and station. 


Av. height, 
in inches. 


Av. No. 
of leaves. 


Av. No. 
of tillers. 


Remarks. 


Oats: 

Lincoln 

Phillipsburg. . 

Burlington. . . 
Wheat: 

Lincoln 

Phillipsburg . . 

Burlington. . . 


7 

3.5 
1.75 

7 
4 
2 


4 

3 

1.5 

4 

3 

1.5 


2.5 

2 



3 
2 



Stand good; crop evenly developed. 
Do. 

Stand good; crop unevenly developed. 

Stand good; crop evenly developed. 
Stand fair; crop evenly developed. 
Stand good; crop unevenly developed. 


Barley: 

Phillipsburg. . 
Burlington. . . 


8 

4.5 
2 


4 
3 

1.5 


3 
2 



Stand good; crop evenly developed. 
Do. 

Stand good; crop unevenly developed. 



at Lincoln, 2.0 at Phillipsburg, and 3.9 at Burlington, However, at Lincoln 
this was distributed over 5 periods (where the rainfall was at least 0.23 inch), 
but at the other stations over only 2 periods. The great water-loss to the 
soil occasioned by high run-off, especially at the Great Plains stations, has 
already been discussed (p. 61). 

Available water-content on April 28 to 30, to a depth of 4 feet, is shown 
in table 25. It may be noted at a glance that the soils at practically all 



Table 25. — Water-content in excess of the hygroscopic coefficient, 1921. 





April 28 to 30. 


May 19 to 21. 


June 9 to 10. 


June 22. 


June 30, Burlington. 


Depth, 
in feet. 


a 
a 


ti 
1 

tn 

a 

1 


S3 

s 

.£ 
pq 


a 

*o 

c 

a 


ti 

a 
% 

P4 


a 

o 

bO 
•S 

Ti 
PQ 


a 
"o 

o 

a 


ti 

u 

£i 

St 

Pm 


o 

bD 

a 

B 
PQ 


d 
o 
a 


ti 
1 

Pw 


to 0.5. . . . 
0.5 to 1 ... . 

1 to 2 


15.6 
16.5 
16.6 


13.9 
12.3 
7.7 


11.2 
9.7 
8.8 


11.9 
15.7 
17.1 


13.1 
12.2 
9.9 


6.6 
7.4 
3.5 


17.5 
16.2 
12.5 


20.7 
14.9 
3.9 


2.7 
1.9 
0.3 


7.6 
9.4 
10.8 


1.0 
5.1 
3.6 


-2 
-1 
-2 


6 
9 
1 


2 to 3 


15.9 


2.7 


2.4 


14.9 


5.4 


i-0.7 


12.9 


4.3 


i-0.4 


10.2 


1.0 


!-l 





3 to 4 .... 


14.0 


3.6 


0.9 


14.7 


5.2 


0.2 


13.9 


5.2 


-0.2 


12.0 


5.0 


-1 


3 



























i The fluctuations of soil-moisture at depths below 2.5 feet slightly above or below the hygro- 
scopic coefficient are due largely to variations in the texture of the soil which occur even at 
the short distances apart at which the samples were taken, and not to actual changes in the 
water-content. 



82 Development and Activities of Roots of Crop Plants. 

depths are progressively drier westward. Abundant moisture was present at 
all levels at Lincoln; the soil below 1 foot was quite dry at Phillipsburg, 
while no available moisture occurred below 3 feet at Burlington. However, 
at all stations the surface soil had been fairly moist during the period, and 
undoubtedly the limiting factor to growth was temperature. 

At Lincoln the mean temperature for April was 53.9° F., at Phillipsburg 
54.2°, and at Burlington 50.4°. The temperature at Lincoln fell below 
freezing on 6 days (latest April 17) during April, at Phillipsburg on 7 days 
(latest April 26), and at Burlington on 13 days, including April 28. The crops 
at the latter station had been damaged somewhat by frost. The soil-tem- 
perature to depths of 4 feet on April 28 to 30 are given in table 26. These 



Table 26. — Soil temperatures, 1921. 





April 28 to 30. 


May 19 to 21. 


June 9 to 10. 


June 22. 


lgton. 


Depth, 
in feet. 


Lincoln. 


Phillipsburg. 


Burlington. 


Lincoln. 


Phillipsburg. 


Burlington. 


Lincoln. 


Phillipsburg. 


Burlington. 


Lincoln. 


Phillipsburg. 


June 30, Burlii 




C. 


°C. 


°C. 


°C. 


°C. 


° C. 


°C. 


°C. 


°C. 


°C. 


6 a 


°C. 


to 0.5... . 


15.4 


24.0 


12.0 


21.0 


20.0 


22.2 


22.5 


21.4 


19.8 


21.2 


23.2 


29.2 


0.5 to 1 ... . 


13.0 


23.1 


11.0 


19.0 


17.8 


15.0 


21.8 


20.2 


18.8 


21.1 


22.4 


26.1 


1 to 2 


12.0 


15.0 


10.5 


13.4 


16.4 


14.0 


20.2 


18.8 


16.8 


20.1 


21.5 


23.9 


2 to 3 


12.0 


14.0 


10.5 


13.1 


15.0 


12.4 


18.6 


17.2 


15.8 


18.8 


21.2 


21.8 


3 to 4 


10.8 


12.0 


10.0 


12.0 


13.5 


11.8 


17.8 


16.0 


15.0 


17.4 


20.5 


20.0 























data show that the drier soils at Phillipsburg were warmer at all depths than 
those at Lincoln, while the Burlington soils were much colder than at either 
of the other stations. 

By May 18 to 21 the wheat and barley at the several stations had reached 
the stages of development shown in plate 5. The condition of the oats in 
the various plats at this time is shown in plate 6. Judging from general 
crop conditions, the growing-season at Phillipsburg was at least a week later 
that than at Lincoln, while that at Burlington was perhaps 3 weeks later. 
A summary of crop development is given in table 27. At both Phillipsburg 



Table 27. — Crop development at the several stations, May 18 to 21, 1921. 



Crop and station. 


Av. height, 
in inches. 


Av. No. 
of leaves. 


Av. No. 
of tillers. 


Remarks. 


Oats: 










Lincoln 


17 


6 


5 


Thick, even growth. 


Phillipsburg . . 


7 


5 


4 


Crop thinner than at Lincoln. 


Burlington. . . 


3 


4 


2 


Crop uniform but thin. 


Wheat: 










Lincoln 


18 


5 


6 


Thick, even growth. 


Phillipsburg. . 


8 


4 


5 


Crop uneven, thinner than at Lincoln. 


Burlington. . . 


3 


3 


3 


Crop uniform but very thin. 


Barley: 










Lincoln 


18 


6 


5 


Thick, even growth. 


Phillipsburg. . 


10 


5 


4 


Crop thinner than at Lincoln. 


Burlington. . . 


3.5 


4 


2 


Crop uniform but thin. 



Investigations at All Stations. 



83 



and Burlington the cereals, and particularly the oats and wheat, had many 
dead or injured leaf-tips, probably the result of local drought, coupled with 
frost injury at the latter station. At all the stations the development of 
the crops checked well with those in adjoining fields, respectively. 

The precipitation during the period (April 28 to May 20) was 3.8, 2.2, 
and 0.7 inches going from Lincoln to the western stations, respectively. 
The available water-content on May 19 to 21 (table 25) occurred in decreasing 
amounts as one proceeded westward. In the first 2 feet of soil the minimum 
supply, which was 12 per cent at Lincoln, fell to 10 per cent at PhilUpsburg 

May June 

1 2 ' 3 4 1 2 3 4 























/ 






ti 


\ 

\ 

— \ 


/ N 






ft 

1 

ft 

1 




w 


fr 

h 


\ 

\ 

\ 

\ 


/ 
/ 

/ 

i 

f 






/// 




w 


m 

\Li 




/ 


/ 


\ 


1 




\ 
\ 




-\ 


/ 

-f— 


// 


\ 


7/7/ 

W- 




^ , 


ft 

/ 


s 

\ 

\ 

\ 

N 


/ 

/ 

/ 

/ 

—t 






II 






— 7 

/ 

/ 

f 


\ 

\ 

\ 


/ 

/ 


/ J 
















X / 
/// 




I 








! 





Fig. 37. — Average day air-temperatures (heavy lines) and average night 
temperatures (light lines) at Lincoln (solid lines), and Phil- 
lipsburg (long broken lines) and Burlington (short broken 
lines), 1921. 

and 4 per cent at Burlington. At a depth of 2 to 4 feet no water was available 
at Burlington, about 5 per cent at Phillipsburg, and 15 per cent at Lincoln. 

Soil-temperatures (except for fluctuations in the surface foot) had increased 
at all stations (table 26) and were more favorable for root development. 
A continuous record of the temperature at a depth of 3 inches in the prairie 
sod was obtained at Phillipsburg and Burlington. The average daily tem- 
perature at PhilUpsburg varied from 55° to 60° F. while at Burlington it 
was rather consistently 5° colder. The daily range at Burlington (12° to 18° 
F.) was also somewhat greater than at the former station. The average day 



84 



Development and Activities of Roots of Crop Plants. 



and night air-temperatures during this interval are shown in figure 37. In 
general, the temperature is highest at Lincoln and lowest at Burlington. 
The low night temperature (45° to 56° F.) is especially significant in con- 
sidering the growth of crops. The lower relative humidity and greater 
wind movement is indicated by the higher evaporation at Phillipsburg and 
Burlington (fig. 38). 

On May 25, the barley at Lincoln began to head out. By the first of June 
all of the crops were fairly well headed and had an average height of 3 feet. 
The wheat and oats continued heading during the first week of June. The 
crops had been blown down badly on May 8 during a heavy rainstorm, 
but recovered more or less completely by June 1, when another storm lodged 
the wheat and barley again. 



May June July 

4 1 2 3 4 1 











J 


V 


- — — • 








/ 
/ 

/ 

/ 
1 


\ 

\ 

\ 

V 

\ 


4 — 




1 

1 

A- 


\ 

\ 

-A — 


1 
1 

I 

1 
1 


\ 

\ 

\ 
\ 
\ 

-A 






/ 
/ 
/ 

/ 

- — J- 


\ 

\ 

\ 
\ 

V— 


1 

1 
1 
I 








1 
1 
i 
i 


\ 

\ 

> 


-1 


\ 

\ 




\^ 
\ 


<-? 






~-V 
\ 




\ 











Fig. 38. — Average daily evaporation at Lincoln (solid line), 
Phillipsburg (long broken lines), and Burling- 
ton (short broken lines), 1921. 



At Phillipsburg the crops headed out about a week later than at Lincoln. 
Moreover, they developed much more irregularly, the barley having an 
average height on June 10 of about 2.7 feet, the oats 2.3 feet, while the wheat 
was only 1.9 feet tall. The latter crop had been rather severely damaged 
by drought; all but the upper two or three leaves were badly discolored or dead. 

At Burlington none of the cereals exceeded a foot in average height on 
June 10, and they did not begin heading out until 10 days later. The effect 
of a scant water-supply was shown by the many dry and dead leaf-tips, 
this being especially marked on the first four or five leaves. It is interesting 
to note that these shorter plants with less extensive foliage had almost as 



Investigations at All Stations. 



85 



many leaves as the taller ones at the other stations. Plate 7 shows the 
relative development of wheat and barley on June 10, while the oat plats 
at the several stations are shown in plate 8. 

Rainfall during this period (May 20 to June 10) was 4.0, 5.7, and 1.7 
inches at Lincoln, Phillipsburg, and Burlington, respectively. The water- 
content of the soil is given in table 25. The well-watered soil at all depths 
at Lincoln (13 per cent or more) contrasts strikingly with the drier subsoil 
at Phillipsburg (5 per cent or less) ; while at Burlington scarcely 2 per cent 
was available in the first foot and none deeper. However, during the inter- 
vening period (May 28), conditions were slightly better, with 4 to 7 per cent 
available moisture in the surface foot at Burlington, while moisture relations 
at Phillipsburg were similar to those indicated in the table. At no time 
at Lincoln was there a period of drought, well-distributed and ample rainfall 
keeping the soil moist. 

The average soil-temperature at a depth of 3 inches was highest at Phillips- 
burg (68° to 72° F.), intermediate at Lincoln (66° to 68° F.), and lowest 
at Burlington (65° to 68° F.). The daily range at Burlington (16° to 20° F.) 
was slightly greater than at either of the other stations. After June 16 all 
of the soil thermograph-bulbs were placed at a depth of 18 inches. At this 
level the weekly fluctuations did not exceed 2° or 3° F., except in the drier 
soils at Burlington, where they were 4° or 5° F. At this depth the average 
weekly temperatures at Phillipsburg varied from 74° to 76° F. (June 16 to July 
3), at Lincoln 70° to 72° F., and at Burlington 66° to 73° F. The temperatures 
at greater soil-depths are given in table 26. It seems clear from these data 
that differences in soil-temperatures at the several stations are so small that 
they exert little effect upon crop-growth, especially after the seedling 
stage has been past. Air-temperatures at all the stations were very much 
higher than during the preceding interval, but the same general relation with 
highest temperatures at Lincoln and the lowest at Burlington prevailed. 
An exception to this was the slightly warmer nights at Phillipsburg during a 
part of the period (fig. 37). Night temperatures at Burlington continued 
low (averages, 55° to 59° F.), the thermograph-pen sometimes falling to 
42° F. The evaporating power of the air during the last week in May was 
practically the same (22 c. c.) at all the stations, but otherwise much higher, 
as usual, at Burlington (fig. 38). 

The crops ripened at Lincoln and Phillipsburg at practically the same time. 
On June 22 and 23, when they were in the early dough stage, the barley alone 
being somewhat further advanced in development, the roots were examined 
and several representative meter-quadrats of each plat were harvested. 
The crops at Burlington, which were considerably damaged by grasshoppers, 
had reached a similar stage of development when they were harvested on 
June 30. The sheaves were shipped to Lincoln, where all were thoroughly 
air-dried in one of the University of Nebraska botanical laboratories, and 
finally weighed. 

Rainfall at both Lincoln and Phillipsburg was light during this interval 
(0.4 inch or less). This is reflected in the water-content of the soil shown 
in table 25. In this connection it should be pointed out that even when the 
crops were mature the soil at a depth of 4 to 7 feet was very moist at Lincoln 
(18.5 per cent) and less so at Phillipsburg (11.1 per cent). This condition 



86 Development and Activities of Roots of Crop Plants. 

is normal for eastern Nebraska (Weaver, 1920), while the moist subsoil at 
the latter station may have resulted from the heavy precipitation (11 inches 
above normal) during 1919. At Burlington a total of 2.3 inches of rain 
fell on June 18 to 21, but by June 30 no moisture was available for growth at 
any level (table 25). 

Soil-temperatures were much higher during this period, especially in 
the drier soils at Phillipsburg and Burlington, where an increase of 4° or 
5° F., even at depths of 3 or 4 feet, occurred. Air-temperatures remained 
relatively high, with the characteristic sequence of day and night temper- 
atures for the several stations already noted (fig. 37). The great range 
of temperature and humidity at Burlington from day to night and the low 
night temperatures were not inducive to rapid growth. Average daily 
evaporation during the period ranged from 24 to 62 c. c. at Burlington, from 
22 to 28 c. c. at Phillipsburg, while at Lincoln it varied from 8 to 17 c. c. 



Table 28. — Relative development of crops, 1921. 











v-i tn 

o o 


CD 

"0 


+3 1- 






Crop and station. 


height. 


No. stalks 
sq. meter. 


No. stalks 
plant. 


length 
ds or panicl 
aches. 


No. of hea 
sq. meter. 


total weigh 
matter pe 
meter. 


king depth. 


:. depth. 




Ave. 


Ave. 
per 


Ave. 
per 


Ave. 
hea< 
in ii 


Ave. 
per 


Ave. 
dry 
sq. 


Wor 


Mas 


Oats: 


feet. 












feet. 


feet. 




3.2 


375 


3.3 


10.5 


283 


792 


2.6 


4.8 


Phillipsburg. . 


2.8 


353 


2.9 


9 


269 


366 


3.0 


5.3 


Burlington. . . 


1.5 


»414 


2.5 


5 


171 


180 


2.2 


2.5 


Wheat: 
















4.3 




3.2 


648 


2.8 


4 


365 


557 


2.5 


Phillipsburg. . 


2.6 


475 


1.8 


3.5 


211 


314 


2.7 


4.5 


Burlington. . . 


1.6 


i419 


1.6 


2.5 


277 


172 


2.2 


2.5 


Barley: 














2.8 


4.6 


Lincoln 


3.1 


384 


3.7 


»3.5 


306 


622 


Phillipsburg. . 


2.8 


253 


2.2 


3.25 


201 


369 


3.1 


6.0 


Burlington. . . 


1.3 


1255 


1.6 


2 


197 


122 


2.0 


2.5 



i Many stalks were only 2 to 4 inches tall and had been dead for some time, 
a Average length of heads without awns. 



Data on the development of the crops at the several stations at the time 
of harvest is given in table 28. An examination of table 28 shows in every 
case, as in 1920, a decrease in height of the crop from the more humid to the 
more arid stations. The same general relation holds for the average number 
of stalks per square meter, except at Burlington, where many tiny stalks, 
only 2 to 4 inches tall, started growth relatively early and soon dried out, but 
remained until harvest. During 1920 the average number of stalks per 
square meter at Burlington was from one-third to one-half less than at the 
other stations, although the number at Phillipsburg often exceeded that at 
Lincoln. The average number of stalks per plant (1921) was in direct rela- 
tion to the water-content of soil and other factors favorable or unfavorable 
to plant-growth. In general, this relation held also during 1920. The 
average number of heads per square meter and the average length of heads 
or panicles decreased from Lincoln to Phillipsburg and Burlington respectively. 



Investigations at All Stations. 



87 



An exception to this occurred in the case of the number of heads of wheat 
at Burlington when compared with Phillipsburg, while the difference in this 
respect in the case of barley was small. However, a clear gradation in the 
reduction of total dry weight from east to west is apparent. Root 
extent, whether working depth or maximum penetration, is least at Burling- 
ton, intermediate at Lincoln, and greatest at Phillipsburg. As pointed out 
elsewhere (p. 76), the very deep root penetration at Phillipsburg is thought 
to be due to an unusually high water-content of the mellow loess soil and 
especially the deeper subsoil. 

Summary of Environment and Crop Development. 

The season of 1921 was one of drought at the Peru station. A deficiency 
of rainfall, coupled with poor distribution, resulted in a much drier soil than 
in 1919, especially the deeper subsoil. The stands of oats, wheat, and barley 
were thin, the plants having tillered poorly, and the height-growth, which 




Fig. 39— Mean precipitation in inches (black) and precipitation for 1921 
at Lincoln (left), Phillipsburg, and Burlington. 

varied from 2 to 2.4 feet, except in the case of barley, was 6 to 8 inches less 
than in 1919. The root systems, except in the case of oats, were somewhat 
less deeply seated than in 1919, reaching working depths of 4 feet and having 
a maximum depth of 6.1 to 6.6 feet. Oat roots were traced to depths of 
8 feet. All of the smaller cereals showed a less marked development of the 
roots into a superficial and a deeply penetrating portion than in 1919. Potato 
roots, while very similar in distribution to those of 1919, showed a lesser 
tendency to turn downward at a later period in their development. This, 
like the lesser penetration of the roots of the cereals, may be due in part to 
the fact that the largest supply of available water occurred in the 1 to 3 foot 
level. Corn, although examined on August 8, had reached the same height 
(8.5 feet) and had approximately the same root depth as on September 2, 



88 Development and Activities of Roots of Crop Plants. 

1919. The root habit was similar to that of 1919, except the lateral spread 
was 8 inches greater (4.7 feet). 

Crops of oats, wheat, and barley were again grown at Lincoln, Phillipsburg, 
and Burlington during 1921, in order to check the results obtained at the 
several stations during the preceding year. The precipitation for the season 
(March to June inclusive) was 1.5 inches below the normal at Lincoln, 0.9 
inch above at Burlington, and 2.0 inches above the normal at Phillipsburg. 
Precipitation for March was approximately half or less than half normal at all 
stations, but April was unusually wet, an excess of 1.8 inches occurring at 
Burlington. During May a deficiency of about an inch occurred at both Lin- 
coln and Burlington, while Phillipsburg had an excess of an inch. During June 
1.3 inches and 0.5 inch of rainfall above the normal occurred at Phillipsburg 
and Burlington respectively, while the rainfall at Lincoln was about normal 
(fig. 39). However, the rains at Lincoln were so well distributed that no 
drought period occurred, while at the other stations these were not infrequent, 
especially at Burlington, where much moisture fell in light showers or torren- 
tial rains. However, the season as a whole was favorable for crop-growth. 

A study of the water-content to a depth of 4 feet (table 25) shows, with an 
occasional exception in the surface foot, a progressively drier soil from Lincoln 
westward. At no time during the growth of the crops was there a deficiency 
of soil-moisture at Lincoln. In fact, a margin of 7.5 to 16 per cent above the 
hygroscopic coefficient usually occurred. Less favorable conditions existed 
at Phillipsburg, where the subsoil (2 to 4 feet) at the time of planting had an 
available moisture-supply of only 3 per cent. This increased during May 
and June to 5 per cent, but was reduced by June 22 to 1 per cent at 3 feet in 
depth. The crops at Burlington had sufficient water above the hardpan 
(3 to 11 per cent) during April and May, but by June 10 this was reduced to 
about 3 per cent, and when the crops were ripe on June 30, no available water 
was present at any depth (c/. Briggs and Shantz, 1912 : 62). 

Average daily soil-temperatures at a depth of 3 inches in the prairie sod 
ranged from 55° to 60° F. at Phillipsburg from April 28 until May 20 and 
about 5° F. lower at Burlington. From May 20 until June 16 the temperature 
was highest at Phillipsburg (68° to 72° F.), intermediate at Lincoln, and 
coldest (65° to 68° F.) at Burlington. Temperatures at a depth of 18 inches, 
after June 16, although quite constant at any station, were also about 6° F. 
lower at Burlington. This general relation held to a depth of 4 feet, although 
differences were so slight that, except in very early spring, they probably 
have little effect upon crop development (table 26). The average day air- 
temperatures (fig. 37) were, as during the preceding season, highest at Lincoln 
and lowest at Burlington, while this same general relation held for average 
night temperatures, those at Burlington varied from 45° to 67° F. 

The average day humidity, in general, held the same relation as during 
1920, viz, being much higher at Lincoln and lower at Burlington than at 
Phillipsburg. The extremes of temperature and humidity at Burlington 
were quite as pronounced as during 1920. The average daily evaporating 
power of the air at the several stations is shown in figure 38. At Burlington 
this sometimes reached a maximum of 45 to over 60 c. c, at Phillipsburg 
28 to 45 c. c, while at Lincoln it did not exceed 18 to 27 c. c. Thus all of the 
environmental conditions for crop-growth were most favorable at Lincoln, 
intermediate at Phillipsburg, and least favorable at Burlington. 



Investigations at All Stations. 



89 



The relative development of the crops at the several stations at different 
periods of growth is shown in plates 5 to 8. A summary of crop development 
during 1921 is given in table 29, where the data of the preceding year are also 
included. 

An examination of table 29 shows that the crops at Lincoln and Phillipsburg 
had as great, and in nearly every case a greater, height-growth in 1921 than 
during the preceding season. At Burlington the height-growth was the same 
for oats during the two years, but less for the other cereals in 1921. The 
average yield of dry matter at the several stations is not only in the same 
sequence as during 1920, but the relative amounts are strikingly similar. 
The working depth of roots is slightly less than during 1920, as is also, in 
general, the maximum depth of penetration. 



Table 29. — Comparison of crop development, 1920 and 1921. 



Crop and station. 


Av. height, 
in feet. 


Av. yield in 
grams per sq. 
meter. 


Working 
depth, in feet. 


Maximum 
depth, in feet. 




1920 


1921 


1920 


1921 


1920 


1921 


1920 


1921 


Oats: 
















4.8 




3.0 


3.2 


706 


792 


2.8 


2.6 


4.8 




2.6 


2.8 


379 


366 


3.3 


3.0 


6.0 


5.3 




1.5 


1.5 


175 


180 


2.7 


2.2 


2.7 


2.5 


Wheat: 


3.2 


3.2 


740 


557 


3.5 


2.5 


4.8 


4.3 




2.3 


2.6 


322 


314 


3.0 


2.7 


5.8 


4.5 




1.7 


1.6 


205 


172 


2.7 


2.2 


2.7 


2.5 


Barley: 


2.7 


3.1 


607 


622 


3.3 


2.8 


5.4 


4.6 




2.4 


2.8 


407 


369 


3.3 


3.1 


6.7 


6.0 


Burlington 


! 1.7 


1.3 


176 


122 


2.5 


2.0 


2.9 


2.5 



Correlation of Crop Development with that of Native 

Vegetation. 

Native plants have the same general requirements as regards heat, light, 
water, etc., as cultivated crops. Since their growth is controlled by the same 
physiological conditions, generally speaking, that hasten or retard the growth 
of crops, the use of the native vegetation as an indicator of the possibilities 
of crop production and as a criterion of average yield in a given plant associa- 
tion is patent. Different environments in agricultural regions should give, 
broadly speaking, similar differences in relative growth, yield, etc., of crop 
plants as of the native vegetation. Thus native plant-growth becomes a 
measure of the effect of all the conditions which are favorable or unfavorable 
for agriculture. Although conditions for growth, as indicated by a plant 
association, can be brought out with sufficient clearness to predict with a fair 
degree of certainty what will happen when crops are planted, the final test 
is the success or failure of the crop when grown (cf. Shantz, 1911). It is 
instiuctive, therefore, to consider the correlation between crop development 
and that of the native vegetation in the range of habitats under which these 
investigations were made. 



90 Development and Activities of Roots of Crop Plants. 

The differences found in the lesser height-growth, smaller yield, and less 
extensive underground parts, going from the more mesophytic eastern stations 
to those of greater aridity westward, correlate directly in nearly every way 
with the growth of native vegetation, whether trees, weeds, or species of the 
native grass land are considered. The native vegetation growing through 
a long period of years integrates the climatic conditions during its growth. 
Thus it is not only an expression of the present conditions, as is true largely of 
rapidly maturing crops, but is to a large extent a record of conditions that have 
obtained during a period of many years. 

The favorable climate for tree-growth at Peru is indicated not only by the 
large number of species present, but also by their development both in diam- 
eter and height. At Lincoln, forests are confined to the flood-plains. The 
species are much fewer in number and the trees are smaller both in diameter 
and height (c/. Pool, Weaver, and Jean, 1918). Only a very few species occur 
along the streams at Phillipsburg, and these are noticeably smaller in every 
way than those at Lincoln, while the few drought-enduring species which 
can grow only under cultivation on the plains at Burlington are even smaller 
of stature. 

The variety and abundance of the weed flora of eastern Nebraska, as well 
as the rank growth of the plants, stand in striking contrast to the paucity of 
species, their lesser abundance, and poorer development at the western 
stations. Very marked differences occur even between Phillipsburg and 
Burlington, low water-content of soil, except in early spring, almost constantly 
inhibiting normal growth at the latter station. Such widely distributed 
species as Grindelia squarrosa and Amaranthus retroflexus reach heights of 3 
or more feet in eastern Nebraska, but are often limited to a growth of 6 to 12 
inches in western Kansas and eastern Colorado. The dwarfing of Festuca 
octoflora and Lappula occidentalis often to 2 inches or less in the buffalo-grama 
sod at Burlington is in marked contrast to their better development under 
more favorable growth conditions. 

The height-growth of the native plant-cover becomes less, in general, from 
Peru and Lincoln westward. This is due in a large measure to the lesser 
abundance or complete disappearance of many of the tall-grass dominants 
in the mixed-prairie association and a greater abundance of buffalo-grass, 
grama-grass, and certain carices, but also to the poorer development of 
many species in the drier habitats. Such diminution in height-growth has been 
noted repeatedly, while actual measurements of a large number of species, 
including Agropyrum glaucum, which ranges throughout the area, shows the 
validity of this statement. A study of the growth of seedlings and transplants 
at the several stations (Clements and Weaver, 1921) affords conclusive proof. 
Similar results were obtained during 1919, when rye, oats, and wheat were 
measured at 14 different stations. Using the height-growth in the true 
prairie as unity, the ratios for mixed-prairie and short-grass plains were as 
follows: rye 100 : 66 : 56, oats 100 : 94 : 85, and winter wheat 100 : 85 : 64. 
Less favorable growth conditions westward are further indicated both by the 
smaller number and poorer development of societies of subdominants in the 
grassland (c/. Clements, 1920). 

The actual plant production of the native vegetation also correlates directly 
with that of cultivated crops. During 1920, 30 square-meter quadrats were 
cut in the undisturbed grassland at each of the several stations. When 



Investigations at All Stations. 



air-dried the vegetation yielded an average of 196 grams per square meter 
at Burlington, 306 at Phillipsburg, and 444 at Lincoln. Wheat-grass, during 
1921, gave an average yield per square meter of 400, 457, and 606 grams respec- 
tively. These data are typical of those obtained during a series of years 
(Weaver, 1921). 

Similar relations hold as regards the extent of the roots of native vegetation. 
The roots of seedling grasses and certain subdominant herbs penetrate the 

Idly and to a greater depth than at Lincoln, 
3st root-growth was recorded. Similarly, 
ivere found to penetrate from 2 to 4 feet 
or Phillipsburg. Regarding the normal 

i several plant associations, the following 

the grass i an( i formation" are instructive. 

~ s of eastern Nebraska, 14 per cent had roots 

m g 3 first 2 feet of soil; 21 per cent were rooted 

* >w 5 feet; while 65 per cent penetrated to 

tetimes to 12 or even 20 feet, 
nixed prairie (hard lands), 11 per cent were 
I S ent were of intermediate depth (2 to 5 feet) , 

I f; extended well below the fifth foot of soil, 

I ™ jet. Of these, 71 per cent are well adapted 

t, g t-face soil only is moist. 

00 ies of the short-grass plains, all but one are 

1 he surface soil. Three are shallow rooted, 
g nd their roots beyond a depth of 5 feet. 

g lepth as one goes eastward from the short- 

£ the deep subsoil is constantly moist is in 

m na de on the root depth of cereals at 14 

® it extent in the true prairie as unity, the 

m short-grass plains was as follows : Working 

5 100 : 95 : 79; winter wheat, 100 : 93 : 61. 

| 50 :65; oats, 100 :94 :77; winter wheat 
«— 

rect correlation may be seen between the 
5 of crops and that of the native vegetation 
onment. 



90 



Development and Activities of Roots of Crop Plants. 



The differences found in the lesser height-growth, smaller yield, and less 
extensive underground parts, going from the more mesophytic eastern stations 
to those of greater aridity westward, correlate directly in nearly every way 
with the growth of native vegetation, whether trees, weeds, or species of the 
native grass land are considered. The native vegetation growing through 
a long period of years integrates the climatic conditions during its growth. 
Thus it is not only an expression of the present conditions, as is true largely of 
rapidly maturing crops, but is to a large extent a record of conditions that have 
obtained during a period of many years. 

The favorable climate for tree-growth at Peru is indicated not only by the 
large number of species present, but also by their development both in diam- 
eter and height. At Lincoln, forests are confined to the flood-plains. The 
species are much fewer in number and the trees are smaller both in diameter 
and height (c/. Pool, Weaver, and Jean, 1918). Only a very few species occur 
along the streams at Phillipsburg, and these are noticeably smaller in every 
way than those at Lincoln, while the few drought-enduring species which 
can grow only under cultivation on the plains at Burlington are even smaller 
of stature. 

The variety and abundance of the weed flora of eastern Nebraska, as well 
as the rank growth of the plants, stand in striking contrast to the paucity of 
species, their lesser abundance, and poorer development at the western 
stations. Very marked differences occur even between Phillipsburg and 
Burlington, low water-content of soil, except in early spring, almost constantly 
inhibiting normal growth at the latter station. Such widely distributed 
species as Grindelia squarrosa and Amaranthus retroflexus reach heights of 3 
or more feet in eastern Nebraska, but are often limited to a growth of 6 to 12 
inches in western Kansas and eastern Colorado. The dwarfing of Festuca 
octoftora and Lappula occidentalis often to 2 inches or less in the buffalo-grama 
sod at Burlington is in marked contrast to their better development under 
more favorable growth conditions. 

The height-growth of the native plant-cover becomes less, in general, from 
Peru and Lincoln westward. This is due in a large measure to the lesser 
abundance or complete disappearance of many of the tall-grass dominants 
in the mixed-prairie association and a greater abundance of buffalo-grass, 
grama-grass, and certain carices, but also to the poorer development of 
many species in the drier habitats. Such diminution in height-growth has been 
noted repeatedly, while actual measurements of a large number of species, 
including Agropyrum glaucum, which ranges throughout the area, shows the 
validity of this statement. A study of the growth of seedlings and transplants 
at the several stations (Clements and Weaver, 1921) affords conclusive proof. 
Similar results were obtained during 1919, when rye, oats, and wheat were 
measured at 14 different stations. Using the height-growth in the true 
prairie as unity, the ratios for mixed-prairie and short-grass plains were as 
follows: rye 100 : 66 : 56, oats 100 : 94 : 85, and winter wheat 100 : 85 : 64. 
Less favorable growth conditions westward are further indicated both by the 
smaller number and poorer development of societies of subdominants in the 
grassland (c/. Clements, 1920). 

The actual plant production of the native vegetation also correlates directly 
with that of cultivated crops. During 1920, 30 square-meter quadrats were 
cut in the undisturbed grassland at each of the several stations. When 



Investigations at All Stations. 



91 



air-dried the vegetation yielded an average of 196 grams per square meter 
at Burlington, 306 at Phillipsburg, and 444 at Lincoln. Wheat-grass, during 
1921 gave an average yield per square meter of 400, 457, and 606 grams respec- 
tively. These data are typical of those obtained during a series of years 

(Weaver, 1921). / ■ . A . 

Similar relations hold as regards the extent of the roots of native vegetation. 
The roots of seedling grasses and certain subdominant herbs penetrate the 
mellow loess soil at Peru more rapidly and to a greater depth than at Lincoln, 
while at Burlington the shallowest root-growth was recorded. Similarly, 
numerous mature prairie plants were found to penetrate from 2 to 4 feet 
deeper at Peru than at Lincoln or Phillipsburg. Regarding the normal 
depth of root penetration in the several plant associations, the following 
data from "Root development in the grassland formation" are instructive. 
Of 43 species studied in the prairies of eastern Nebraska, 14 per cent had roots 
which seldom extended beyond the first 2 feet of soil; 21 per cent were rooted 
well below 2 feet but seldom below 5 feet; while 65 per cent penetrated to 
depths greater than 5 feet and sometimes to 12 or even 20 feet. 

Among 36 species excavated in mixed prairie (hard lands), 11 per cent were 
rather superficially rooted, 45 per cent were of intermediate depth (2 to 5 feet), 
and 44 per cent had roots which extended well below the fifth foot of soil, 
many in fact to a depth of 7 to 9 feet. Of these, 71 per cent are well adapted 
to absorb water even when the surface soil only is moist. 

Of 8 of the most important species of the short-grass plains, all but one are 
adapted for water absorption in the surface soil. Three are shallow rooted, 
and only one or two normally extend their roots beyond a depth of 5 feet. 

This increasingly greater root depth as one goes eastward from the short- 
grass plains into regions where the deep subsoil is constantly moist is m 
agreement with determinations made on the root depth of cereals at 14 
stations during 1919. Using root extent in the true prairie as unity the 
relative depth in mixed-prairie and short-grass plains was as follows : Working 
depth of rye, 100 : 92 : 69; oats, 100 :95 :79; winter wheat, 100:93 :61. 
Maximum depth of rye, 100:90:65; oats, 100:94:77; winter wheat 

100 : 80 : 51. , +u 

From the foregoing data a direct correlation may be seen between the 
development of the tops and roots of crops and that of the native vegetation 
growing in the same general environment. 



92 Development and Activities of Roots of Crop Plants. 

VI. DEPTHS AT WHICH PLANTS ABSORB WATER 
AND NUTRIENTS. 

Repeated examination of developing root systems of plants during the past 
six years (Weaver, 1915, 1917, 1919, 1920), together with the usual findings 
of great depth of penetration where growth conditions were favorable, have 
led the writers to gravely doubt the accuracy of statements current in the 
literature on soils regarding the depth at which plants absorb. The common 
viewpoint is well stated as follows in one of our best modern works (Russell, 
1917 : 56). 

"It is well known that only the top 6 or 8 inches of the soil is suited to 
plant life, and that the lower part, or subsoil, plays only an indirect part in 
plant nutrition. We shall, therefore, confine our attention almost exclusively 
to the surface layer." 

It seems certain that in many of our native grassland species which possess 
strong tap-roots with little or no branching in the surface foot or two of soil, 
little if any absorption occurs in these soil layers, because of the cutinized 
or suberized root cortex. Rosa arkansana, Kuhnia glutinosa, Liatris punctata, 
and Amorpha canescens are common examples. Among cultivated crops, 
life-history studies indicate that older alfalfa and sweet-clover plants, for 
example, are very similar to the preceding in this regard. Even among 
fibrous-rooted species, including cereals, it must be kept distinctly in mind that 
the number of roots in any given area of soil is no criterion of their activity. 
It seems probable that with increasing age the older roots are cutinized or 
suberized, and unless new branches are put out, the seat of maximum absorbing 
activity is transferred to soil layers of ever-increasing depth, inhabited by the 
younger parts of the root system. While it is clear that many new roots 
develop in the surface soils, especially from plants that tiller, and that older 
ones normally develop abundant laterals, yet it seems equally certain that the 
bulk of the surface roots are developed earlier in the life of the plant and 
because of age and consequent structural changes must be less active absorbers 
at a time when rapid development of a network of new roots is occurring at 
greater depths. A casual perusal of the preceding pages should impress the 
reader with the great depth to which certain crops penetrate and with the 
abundance of roots below the level of cultivation (6 to 8 inches). Extended 
examinations of the root distribution of winter wheat and rye at 10 different 
stations in true-prairie and mixed-prairie areas of Nebraska, Kansas, and 
South Dakota show conclusively their deep-rooting habits. The average 
maximum depth attained by these cereals was 5.0 and 5.1 feet respectively, 
while the average working depth (the soil-level to which the bulk of the roots 
penetrate and consequently where they are very abundant) was 3.7 feet for 
wheat and 3.9 feet for rye. Other crops, such as red clover and alfalfa, were 
found to be rooted very much deeper (Weaver, 1920). In fact, in nearly all 
cases where the roots of crop plants were excavated, the total development 
below the cultivated soil-layer was as great and usually much greater than 
that in the surface soil. Among native plants, the bulk of the root system in 
the great majority of cases lies below the surface foot, and the same holds true 
for many crop plants, including especially the fall-planted cereals. The de- 
pendence of plants upon the deeper-seated portion of their root systems is 



Depths at Which Plants Absorb Water and Nutrients. 93 



well illustrated in times of drought, where the vegetation remains unwilted 
and crops do fairly well even after the water in the surface 6 inches of soil has 
been nearly or entirely exhausted. 

Preliminary Experiments. 
During 1919, preliminary experiments were conducted in the greenhouse 
at the University of Nebraska. White Kherson oats was grown in con- 
tainers 1.5 feet in diameter and 2.5 feet deep. These were filled with a 
fertile loam soil at an optimum and uniform water-content. The experiment 
extended from February 4 to April 1. The soil, both in the containers with 
plants and those without plants (used for checks), was sampled for water- 
content at intervals of 14 days. During the period of March 4 to 18, when 
the plants were 28 to 42 days old, a marked loss of water (3.5 to 8.3 per cent) 
was determined at depths of 1 to 2.5 feet in the containers with plants, while 
the controls lost only 1.3 per cent at the 1.5-foot level and none at greater 
depths Similar results were obtained for the following two weeks' interval, 
at the end of which (April 1) the plants, then 12 inches tall, were unearthed. 
Root distribution in the deeper soils corresponded with the amounts of water 
removed at the various levels. 

Such experiments, while indicative, are subject to two fundamental criti- 
cisms. Drought in the surface soil might result in a deeper penetration of 
roots while water from lower levels might move to higher ones which have 
been more or less depleted of their supply, either from evaporation or from 
absorption by the plants. Thus less absorption might take place at deeper 
levels than the water-content samples would indicate. Moreover, in its 
upward or downward movement, nutrients might be carried from one level 
to another by the water. Although the capillary movement of water m 
soils has been shown by Alway (1913, 1917), Burr (1910), and others to be 
much less than formerly supposed, experiments were devised to check out 
all movements of either water or nutrients from one soil-layer into another, 
except through the roots. In filling the containers, the soil, after being 
brought to the desired water-content, was firmly compacted and then sealed 
with a layer of wax. This consisted of 85 per cent paraffin or parowax and 
15 per cent petrolatum (Briggs and Shantz, 1912). The seal was applied 
hot, so that it penetrated a little into the soil, and when it cooled clung tena- 
ciously to the soil particles. It varied from 2 to 3 mm. m thickness When 
it had cooled and hardened, another layer of soil, usually 6 to 12 inches 
thick, was added, and the process repeated until the container was filled. Oats, 
barley, and other plants were grown in containers where the soil was thus 
separated into hermetically sealed layers of varying thickness The roots 
of plants grown in these soils were distributed evenly throughout the soil- 
mass, penetrating the wax layers without difficulty. In fact, no external 
differences could be noted between roots growing through the seal and those 
in ordinary soil (plates 9 B and 9 c). . . Al , ' 

This method furnishes at once a means of determining the amount of 
water or nutrients removed at any given level to which the roots penetrate. 
Moreover, by using a series of containers in which plants of the same age 
are grown, it is possible by opening containers from time to time to determine 
the absorbing activity of the roots at the various levels at any stage in the 
development of the crop. 



94 



Development and Activities of Roots of Crop Plants. 



Field Experiments, 1920. 

During the spring and summer of 1920, experiments were conducted to 
determine more precisely the water-absorbing power of crop-plants at various 
soil-levels. Barley was employed and the crop was grown under field con- 
ditions adjoining the crop-plats already described on the lowland area at 
Belmont. 




9 10 11 12 13 14 i& 



Fiq. 40. — Diagram of containers and development of barley, 1920. Positions of wax seals, 
6 inches apart, indicated by cross-lines. 

Containers of large size and especially designed for ease of root examina- 
tions were used. The larger ones, in which the crops were grown for long 
periods or to maturity, were cylindrical in shape, 1.5 feet in diameter, and 3.5 
feet deep. They consisted of heavy galvanized sheet-iron rolled into a 
cylinder, with an overlap on the edge of 5 inches, fitted into a one-piece cir- 
cular bottom with an upright edge of 0.5 inch, and held in place by three 



Depths at Which Plants Absorb Water and Nutrients. 



95 



metal hoops fastened with small bolts. When filled with firmly com- 
pacted soil, the smooth overlapping edges fit tightly, while at the end of the 
experiment the whole core of soil could easily be exposed for examination by 
simply removing the bottom of the containers and the hoops (plate 9, a and b). 
Plants grown for shorter periods were in containers of the same design, but 
with a diameter of 1 foot and a depth of either 2 or 2.5 feet. In this experi- 
ment 16 containers were used, but the plants in one were accidentally de- 
stroyed. 

On May 19 to 21 two long trenches were dug to a depth of 2 to 3.5 feet, 
the rich, alluvial, silt-loam soil being kept separate from the somewhat more 
clayey subsoil. The containers were then placed in a row in the trenches 
about 6 inches apart, the lower end of each container resting evenly upon 
its inverted bottom. The soil which had been removed from the trench was 
next mixed very thoroughly by shoveling it back and forth on an improvised 
platform. It was in excellent tilth, with a water-content of about 30 per cent. 
The subsoil, similarly treated on a separate platform, had approximately the 
same water-content. After mixing, the subsoil and surface soil were slowly 
poured into the containers and continuously tamped, so that they were com- 
pacted to a degree not unlike that of the natural soil in the adjoining plats, 
where roots were repeatedly excavated. When filled, the soil in each con- 
tainer was again at approximately the same level it had formerly occupied. 
In filling the containers, duplicate samples were taken at the several levels 
(mostly at 6-inch intervals) for water-content. Moreover, at the time of 
filling, wax seals were inserted in about one-half of the containers between the 
several layers of soil at intervals of 0.5 foot, beginning at 6 inches depth. 
Finally, each container was fitted with a sloping wooden roof, the soil having 
been mounded up so as to fit snugly under the roof. Thus no rain could enter 
except through a central slit three-fourths inch wide and with a length equal 
to the diameter of the container, 1 or 1.5 feet respectively. Through this 
opening barley was planted thickly at a depth of 1.5 inches on May 19, but 
in only the odd-numbered containers, the ones with even numbers being 
used as checks. The trench about the containers was refilled, the soil thor- 
oughly compacted and ridged up in such a manner that drainage was away 
from the disturbed area, the surface-water being carried away through 
shallow ditches about 2 feet distant on either side of the original trench. 
Grass was allowed to grow on this disturbed area which adjoined the crop 
plats. At four periods during June and July, when the crop was in various 
stages of development, certain containers were removed, and the root dis- 
tribution and the water-content determined. The size and arrangement 
of containers and the position of the seals, as well as the relative heights and 
root development of the several plant-groups at the time of examination, 
are shown in figure 40. 

On May 25 to 27, when the barley was about an inch high, the plants 
were thinned to 20 and 25 in each of the small and large containers respectively. 
By June 4 they had reached a height of 4 inches and practically all had 3 or 4 
leaves. The much more rapid development of this late-planted crop than 
that sowed April 9 (p. 41) is clearly correlated with environmental conditions 
which have already been discussed (cf. p. 44 and fig. 20). On June 15 the 
plants were 6 to 8 inches high; some had 2 or 3 tillers. At this time they were 



96 Development and Activities of Roots of Crop Plants. 

again thinned and containers 1, 2, 3, and 4 were removed from the trench and 
examined, while soil samples were obtained, by the use of a geotome, from 
containers 5, 9, 10, and 11. After securing the samples the holes left by the 
soil-tube were carefully refilled with moist soil, which was tamped into place. 



Table 30. — Water-content of soil on May 19 and June 15. 



Container. 


Depth of sample. 


- 

T\/T ntr 1Q 

iviay ±y. 


June lo. 


OSS. 




feet. 


p. ct. 


p. ct. 


p. ct. 




U to U./ 


oU . o 


oo ^ 


ft Q 

O . O 




V. i tO l.O 


Oft ft 
ZO . O 


OA K 
zo . o 


Q 
4 . o 




1.3 to 2 


26.9 


25.2 


1.7 


JNo. 3 


u to u.o 


97 7 
Z< . i 


o^ 


4 2 




u.o to 1 


Oft Q 


Oft 1 


2.2 




1 to 1.0 


07 Q 
Z i . y 


07 1 






l.o to ^ 


op; q 
ZO . V 


Oft 1 
ZO . 1 


TU . z 


"NT— C 


utou./ 


OQ Q 

zy . o 


1R ft 






0.7 to 1.3 


31.5 


26.5 


5.0 




1.3 to 2 


31.2 


28.0 


3.2 


TVTy. n 


u to U.O 


oU . 'k 


04. ft 
zt . o 


K ft 
o . o 




0.5 to 1 


28.6 


24.9 


3.7 




1 to 1.5 


28.5 


25.9 


2.6 




1 K +n O 

l.O to z 


OQ ft 

zy . o 


07 ft 

£ 1 . O 


o n 




z to Z.O 


OQ ft 

zy . o 


oq n 
^y . u 


n s 

w . o 




Z.o to O 


Oft 4 
Zo . *t 


OQ 

zy . o 


1 h Q 

t^u . » 




3 to 3.5 


27.2 


27.8 


+0.6 


JNO. 11 ... . 


u to u.o 


QO F. 
oZ . O 


04. 4 
z^t . t 


s i 

O . 1 




u.o to 1 


Q1 ft 
di . O 


03 7 


ft 1 




1 to l.O 


Qrt J. 
OU . "1 


03 n 

Zo . U 


7 4 




l.o to Z 


3Q ft 
oU . O 


Oft ft 
Zo . o 


o n 
z . u 




z to Z.O 


07 7 
Z/ . / 


Oft Q 
Zo . O 


i n ft 




Z.O tO O 


07 7 
Z/ . / 


07 3 
Z / . O 


n 4 

U . ^: 




3 to 3.5 


27.6 


27.3 


0.3 


No. 2 


to 0.7 


29.5 


31.1 


+ 1.6 




0.7 to 1.3 


29.6 


30.6 


+ 1.0 




1.3 to 2 


31.9 


32.4 


+0.5 


No. 4 


to 0.5 


27.1 


28.2 


+ 1.1 




0.5 to 1.0 


28.0 


28.6 


+0.6 




1.0 to 1.5 


28.6 


28.3 


0.3 




1.5 to 2 


28.6 


29.0 


+0.4 


No. 10 


to 0.5 


27.2 


27.8 


+0.6 




0.5 to 1 


27.0 


27.6 


+0.6 




1 to 1.5 


28.3 


28.0 


0.3 




1.5 to 2 


28.1 


27.8 


0.3 




2 to 2.5 


27.4 


27.8 


+0.4 




2.5 to 3 


30.5 


30.3 


0.2 




3 to 3.5 


30.2 


30.1 


0.1 



The water-content at the various levels, together with the loss during the 
period, may be seen in table 30. These data, with a statement of root dis- 
tribution, are summarized in table 31, while the actual root distribution is 
shown diagrammatically in figure 40. 

An examination of table 30, and especially table 31, shows that the water- 
content in the several containers with plants had been reduced from 4 to 10 



Depths at Which Plants Absorb Water and Nutrients. 



97 



per cent in the surface 6 or 8 inches, from 2 to 8 per cent in the second 6 or 8 
inches, from 1 to 7 per cent in the third 6 or 8 inches, and from to 2 per cent 
in the next 6-inch layer. Below 2 feet depth no change in water-content had 
occurred that could not be easily accounted for by variations in soil sampling. 
These losses are clearly correlated with root distribution, for although the 
plants were only 27 days old, the roots were very abundant not only in the 



Table 31. — Water lost during the period May 19 to June 15. 



Con- 
tainer. 


Percentage of water removed at various depths, in feet. 


Remarks. 


to 0.5 


0.5 to 1 


1 to 1.5 


1.5 to 2 


2 to 2.5 


2.5 to 3 


3 to 3.5 


No. 1 . . 

No. 3. . 

No. 5.. 4 
No. 9.. 4 
No. II. 4 
No. 2 . . 
No. 4. . 
No. 10.. 


*8.3 
4.2 

no. 5 

5.8 
8.1 
1+I.6 
+11 
+0.6 


«2.3 

2.2 

2 5.0 
3.7 
8.1 

2 + 1.0 

+0.6 
+0.6 


n.7 

0.8 

3 3.2 
2.6 
7.4 
3 +0.5 
0.3 
0.3 










14 plants; some roots 
penetrated 2 feet but 
were not abundant be- 
low 1.5 feet; soil to 16 
in. well filled with 
roots. 

10 plants; root distribu- 
tion approximately as 
in No. 1, but fewer. 

20 plants. 

About 15 plants. 

About 20 plants. 

■ No plants. 


+0.2 














2.0 
2.0 


0.8 
+0.6 


+0.9 
0.4 


+0.6 
0.3 


+0.4 
0.3 








+0.4 


0.2 


0.1 



1 Samples taken at depth of to 0.7 foot. 3 Samples taken at depth of 1.3 to 2 feet. 

2 Samples taken at depth of 0.7 to 1.3 foot. 4 Soil-tube holes refilled, plants undisturbed. 



surface, but also at depths of 8 to 16 inches, while some penetrated to 2 feet. 
This root development is altogether in agreement with that of barley grown 
in field plats. Moreover, the root distribution in the container with the wax 



Table 32. — Water-content of soil at the several intervals. 









Water-content. 




Container 


Depth of 


Loss, May 19 






Loss, June 15 


No. 


sample. 


to June 15. 






to 28. 






June 15. 


June 28. 






feet. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


5. 


to 0.7 


10.5 


18.8 


14.5 


4.3 




0.7 to 1.3 


5.0 


26.5 


16.4 


10.1 




1.3 to 2 


3.2 


28.0 


13.0 


15.0 


6 


to 0.5 




125.1 


24.8 


0.3 




0.5 to 1 




27.8 


26.9 


0.9 




1 to 1.5 




28.0 


27.2 


0.8 




1.5 to 2 




26.5 


26.3 


0.2 




2 to 2.5 




26.0 


26.8 


+0.8 



1 Water-content at all levels in this container is for May 19. 



seals was identical, so far as could be determined, with that in the unsealed 
soil. Even the most delicate root-ends showed no external differences where 
they encountered the wax seal. 



98 Development and Activities of Roots of Crop Plants. 

On June 28, when the plants had an average height of about 10 inches, 
containers 5 and 6 were removed (fig. 40). A glance at table 32 shows that 
the seals in the check container were preventing appreciable water-loss, while 
any intake in the surface 6 inches had apparently been balanced by evapora- 
tion. During the interval of 13 days since the last examination of container 
5, 4 per cent of water had been lost from the surface 8 inches, but this was 
less than half the absorption from the 8 to 16 inch level, while 15 per cent 
had been absorbed from the 1.3 to 2 foot depth. Clearly, the roots at this 
stage of development were more active in the deeper soil. Unfortunately 
the 2 to 2.5 foot samples were lost in drying. The roots of the 20 plants in 
this container extended to the 2.5 foot-level and were very abundant at a 
depth of 2 feet. These data indicate that the surface roots were much less 
actively absorbing than the deeper, younger portions. The loss in the top 
8-inch layer may be accounted for in part by new roots from the tillers, as 
well as from the parent plant. Considerable water was still available at all 
depths, since the hygroscopic coefficient is rather uniformly about 10 per 
cent (cf. table 10). 

On July 16, containers 9, 10, and 11 were excavated, opened, and examined. 
The plants were about 2.3 feet tall, had tillered extensively, and were in the 
early milk stage. The roots were uniformly distributed throughout the soil, 
except that they were less abundant at depths of 2.8 to 3.5 feet, i. e., below 
the working level (fig. 40). An examination of table 33 (sixth column) shows 



Table 33. — Water-content of soil at several intervals to July 16. 



Container. 


Depth of 
sample. 


Loss 
May 19 to 
June 15. 


Water- 
content 
June 15. 


Water- 
content 
July 16. 


Loss 
June 15 to 
July 16. 


Loss 
May 19 to 
July 16. 




feet. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


No. 9 1 


to 0.5 


5.8 


24.6 


18.6 


6.0 


11.8 




0.5 to 1 


3.7 


24.9 


18.9 


6.0 


9.7 




1 to 1.5 


2.6 


25.9 


16.4 


9.5 


12.1 




1.5 to 2 


2.0 


27.8 


16.3 


11.5 


13.5 




2 to 2.5 


0.8 


29.0 


18.7 


10.3 


11.1 




2.5 to 3 


+0.9 


29.3 


17.9 


11.4 


10.5 




3 to 3.5 


+0.6 


27.8 


25.7 


2.1 


1.5 


No. ll a 


to 0.5 


8.1 


24.4 


16.8 


7.6 


15.7 




0.5 to 1 


8.1 


23.7 


15.7 


8.0 


16.1 




1 to 1.5 


7.4 


23.0 


16.8 


6.2 


13.6 




1.5 to 2 


2.0 


28.6 


16.7 


11.9 


13.9 




2 to 2.5 


+0.6 


28.3 


16.8 


11.5 


10.9 




2.5 to 3 


0.4 


27.3 


21.4 


5.9 


6.3 




3 to 3.5 


0.3 


27.3 


25.5 


1.8 


2.1 


No. 10 3 


to 0.5 


+0.6 


27.8 


29.3 


+ 1.5 


+2.1 




0.5 to 1 


+0.6 


27.6 


27.9 


+0.3 


+0.9 




1 to 1.5 


0.3 


28.0 


27.8 


0.2 


0.5 




1.5 to 2 


0.3 


27.8 


27.2 


0.6 


0.9 




2 to 2.5 


+0.4 


27.8 


28.4 


+0.6 


+ 1.0 




2.5 to 3 


0.2 


30.3 


29.3 


1.0 


1.2 




3 to 3.5 


0, 


30.1 


28.9 


1.2 


1.3 



1 Eleven plants, mostly with 3 to 7 tillers; 2.3 feet tall and in the milk stage. 

2 Twelve plants, mostly with 3 to 5 tillers each, some with 7; about 2.3 feet tall and in milk 
stage. Roots uniformly distributed, except not so abundant in last 6 to 9 inches. 

3 No plants. 



Depths at Which Plants Absorb Water and Nutrients. 



99 



little change in water-content of the check container (No. 10) during the inter- 
val from June 15 to July 16, but a marked loss from the ones with crops, espe- 
cially at depths of 2 to 3 feet. Thus, the activity shown by the deeper portions 
of the roots on June 28 is here confirmed. Indeed, the total water absorbed 
at the several levels (May 19 to July 16) is about the same in amount to a 
depth of 3 feet (table 33, last column). Further evidence for this conclusion 
is given in table 34, which shows the water-loss from the sealed containers 7 
and 8 during this interval. 

Table 34. — Water-content of sealed containers, May 19 and July 16. 



Container No. 7, eight plants, roots quite uniformly- 


Container No. 8. no olants. 


distributed throughout the container. 








Depth of sample. 


May 19. 


July 16. 


Loss. 


May 19. 


July 16. 


Loss. 


Jeet. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


p. ct. 


to 0.5 


25.6 


15.9 


9.7 


26.0 


28.3 


+2.3 


0.5 to 1 


25.7 


14.3 


11.4 


28.1 


27.9 


0.2 


1 to 1.5 


26.3 


16.4 


9.9 


29.5 


30.0 


+0.5 


1.5 to 2 


26.9 


20.7 


6.2 


29.0 


30.4 


+ 1.4 


2 to 2.5 


28.3 


22.8 


5.5 


28.2 


28.7 


+0.5 



On July 29 the barley was nearly ripe. The plants in the remaining con- 
tainers were 2.2 feet tall and were rather badly rusted with Pvxcinia graminis 
tritici. The roots in both the sealed and unsealed soil were rather uniformly 
distributed to near the bottom of the containers, a depth of 3.5 feet. Only in 
the deepest soil were they less numerous. The plants had tillered extensively 
and the dense mat of roots was most pronounced to a depth of 2 feet. None of 
the 4 containers had been disturbed in any way since May 21, except that on 
June 28 a liter of water was slowly added to each through the slit in the roof 

Table 35. — Total water lost at the several levels from May 21 to July 29. 



Depth of 
sample. 



feet. 

to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 
2.5 to 3 

3 to 3.5 



Container No. 12. 



p. ct. 
30.9 
32.0 
31.8 
30.4 
30.4 
31.3 
30.6 



p. ct. 
28.3 
30.4 
30.7 
30.6 
30.3 
31.3 
31.8 



p. ct. 
2.6 
1.6 
1.1 

+0.2 
0.1 
0.0 

+ 1.2 



Container No. 14. 1 



p. ct. 

32.6 
33.3 
33.0 
32.0 
31.7 
32.9 
30.6 



p. ct. 

30.2 
33.0 
33.6 
32.9 
32.5 
31.9 
30.3 



p. ct. 
2.4 
0.3 
+0.6 
+0.9 
+0.8 
1.0 
0.3 



Container No. 13.* 



p. ct. 

32.5 
34.5 
32.7 
34.0 
33.7 
32.6 
30.8 



p. ct. 
13.5 



p. ct. 
19.0 
17.8 
16.4 
16.6 
13.2 
9.1 
6.9 



Container No. 15. 3 



p. ct. 
33.3 
33.3 
31.5 
32.5 
31.9 
31.5 
34.6 



p. ct. 
13.1 
14.5 
15.8 
16.9 
17.9 
19.5 
23.3 



p. ct. 
20.2 
18.8 
15.7 
15.6 
14.0 
12.0 
11.3 



1 No plants. 

* Eight plants, average height 2.2 feet; 2 to 6 tillers each; roots normally distributed to 
bottom of container. 

•Fifteen plants, average height 2.2 feet; 2 to 8 tillers each; roots normally distributed to 
bottom of container. 



100 Development and Activities of Roots of Crop Plants. 



of the container. The total water lost at the several depths, both by the 
sealed and unsealed checks and by the cropped containers, is shown in table 35. 
Allowing for losses from the surface layer by direct evaporation (as indicated 
by the checks), the water removed by absorption is quite uniform in amount 
(about 16 to 18 per cent) to a depth of 2 feet. Below this level it gradually 
diminished in amount to the maximum depth, but even below 3 feet a large 
amount of water was removed. The movement of water by capillarity plays 
a rather unimportant role in replenishing water at the various levels from 
those adjacent, as may be inferred from the water relations of unsealed con- 
tainers when compared with those where such movement was prevented by the 
wax seaL 

Greenhouse Experiments, 1920-21. 

During the fall of 1920 another series of experiments was started in the 
greenhouse at the University of Nebraska, with the object of determining the 
depth at which crop plants remove nutrients from the soil. On October 16, 
44 bags of soil, each weighing about 125 pounds, were secured from the upland 
experimental plats about 3 miles north of Lincoln (p. 40). The mechanical 
and chemical analyses of this soil to the depth to which it was removed (4 feet) 
are given in tables 8 and 9. In securing the samples, two large rectangular 
trenches were dug and the soil removed from the first, second, third, and fourth 
foot and bagged separately. 

Twelve large containers were employed for growing the crop. These 
were the same as those used in the field experiment, except that the smaller 
ones were enlarged so that all had a depth of 3.5 feet. Five had a diameter 
of 1.5 feet, while the others were only 1 foot wide. Before filling the containers 
the soil from each level was spread out on the cement floor of the greenhouse 
and worked over until all lumps were broken up and the soil thoroughly mixed. 
Water was slowly added as the mixing proceeded until the water-content was 
at an optimum, and, after standing for a period, uniformly distributed through- 
out the soil mass. 

The nutrients used in this set of experiments were limited to nitrates for 
several reasons. Nitrates, unlike phosphates and potash, are not adsorbed 
by soil and can be completely recovered by simply leaching with water. 
Consequently a known quantity could be added to the soil when the con- 
tainers were filled, and its use by the plant determined by a chemical analysis 
of. the soil after the containers were opened. Not being adsorbed, they can be 
expected to diffuse readily throughout the soil along with the movement of 
water. They are used in comparatively large quantities by such crops as 
barley, which was employed in this experiment, and hence the error in deter- 
mining by analysis the percentage used by the plant is reduced to a minimum. 
Furthermore, the presence or absence of an abundance of nitrates is shown by 
the foliage of the plant in a striking manner. 

The soil was impregnated with sodium nitrate at the rate of 400 parts per 
million (i. e., 292 parts per million of N0 3 ) before it was placed in the con- 
tainers. This was accomplished by weighing the amount of thoroughly 
pulverized and well-watered soil necessary to fill a container to a depth of 1 
foot when compacted and adding to this the proper amount of salt in a dry 
state. The soil was again thoroughly mixed after the salt was added. 



Depths at Which Plants Absorb Water and Nutrients. 101 



Thus the total nitrate-content at the beginning of the experiment was that 
of the impregnation plus that already in the soil as it came from the field. 
After the water-content of the soil had been determined, the amount of 
NO 3 used in fertilizing was calculated to the dry basis for each respective 
level and these figures were used in the tabulations. 

The containers were placed a few inches apart on the cement floor, and 
after soil from the fourth foot was tamped into the bottom 8 inches of each, 
the usual wax seal was applied. The soil from the third, second, and surface 
foot was then placed in its relative position in each container in a similar 
manner, the several layers being separated by wax seals. The containers 
were filled in pairs, any two in a pair being exactly alike regarding the position 
of the impregnated soil, etc., except that one was provided with apparatus for 
aerating the soil at the four separate levels. This consisted of eight thick- 
walled glass tubes about a centimeter in diameter also placed in pairs, one on 
each side of the container, and of such length that they extended from the 
surface where they were kept corked, well into the first, second, third, or 
fourth foot of soil respectively. Thus by removing the corks and attaching 
a large exhaust pump to one tube of the pair, moist air could readily be 
drawn through the hermetically sealed layer of soil. All the even-numbered 
containers were thus provided for aeration. 

The soil in containers 1 and 2 was impregnated with nitrates in the first 
foot only; in 3 and 4 in the second foot; in 5 and 6 in the third foot; in 7 and 8 
in the fourth foot; that in 9 and 10 was furnished with the salt at all levels, 
while none was added to the soil in containers 11 and 12. 

Before adding the surface seal, two thin strips of wood, about 1.5 inches in 
width, were placed edgewise across the containers and partially sunken in the 
soil in such a manner that the seal was prevented from covering an area of 
soil about 1.5 inches wide extending across the container. In this soil Man- 
churia barley was planted thickly on November 4, after which it was covered 
to a depth of about an inch with dry sand to retard water-loss from the 
unsealed surface. The wax seal was then covered with 2 inches of sand and 
the whole top of each container covered with white oilcloth provided with an 
opening 1.5 inches in diameter to permit the exit of the plants. The covering 
was added to exclude any water which might leak through the greenhouse 
roof during storms or condense on the inner side and drip down. Finally, 
an inclosure nearly 4 feet high was built around the containers and the whole 
filled with sand. This insured a more uniform soil-temperature about the 
developing roots, while barley grown in the sand about the containers, as well 
as on the adjoining benches, helped to keep atmospheric conditions more 
nearly comparable with those in the field. The general arrangement of the 
containers, etc., as well as the development of the crop on December 23, is 
shown in plate 9 d. 

The seed germinated well and the crop was so thick and developed so rapidly 
that it was necessary to thin it by pulling up some of the seedlings from time to 
time during the first month after planting. Half of the containers were 
aerated regularly at intervals of 10 to 14 days until the end of the experiment 
on March 12, although at no time did the aerated plants as a group show a 
more marked growth than the unaerated ones. However, the presence of 
the nitrates had such a pronounced effect upon the growth and color of the 



102 Development and Activities of Roots of Crop Plants. 

barley that two weeks after germination the plants in containers with sodium 
nitrate in the first foot of soil were readily designated by a number of unin- 
terested observers. The difference in growth on December 11 in the unfer- 
tilized soil of container 12 and that of container 1, where the first foot was 
enriched with nitrates, is shown in plate 10. At this time a few of the plants 
had begun to tiller and by December 20 many of the new shoots had three 
leaves. The plants stood up well, although considerably attenuated because 
of the low light intensity, while throughout the experiment the more abundant 
foliage, broader leaves, and darker green color marked the containers with 
nitrates added in the first and second feet. 

On December 21 container No. 5 was taken down and the root system 
examined. The plants averaged 8.5 inches in height (maximum 14 inches), 
but the roots were abundant in the first foot of soil only, a few having pene- 
trated a distance of only 4 to 6 inches into the second foot. Thus, during this 
period of 47 days, the above-ground parts had developed scarcely further 
than plants grown in the field for only 27 days, while the root extent was not 
much more than half as great (table 31). 

From January 18 to February 22 the crops were watered from time to time 
through the opening in the oilcloth cover and wax seal. Water was added 
slowly, so that it penetrated the sand between the wooden strips bordering the 
wax seal and entered the soil below. In this manner a total of 4 liters was 
added to each of the larger containers and 3.1 liters to each of the smaller ones. 

Late in February, the crop, although very short, began to head, but growth 
proceeded so slowly that by March 12 only a few heads had appeared and none 
had blossomed. The development of the crop at this time is summarized in 
table 36, while plate 11 illustrates the difference in growth in the fertilized 
and unfertilized soils. 



Table 36. — Development of crop, March 12. 



Con- 
tainer. 


Height 
in inches. 


Max. 

No. 
leaves 

per 
stalk. 


Width of 
leaves in mm. 


Color. 


No. 
of 
heads. 


Av. 


Max. 


Av. 


Max. 


No. 1.. 


14 


19 


7 


13 


19 


Dark green 


1 


No. 2.. 


13 


18 


8 


13 


18 


Do. 


2 






No. 3.. 


12 


17 


5 


11 


14 


Do. 





No. 4.. 


12 


14 


7 


13 


19 


Do. 


5 


No. 6. . 


10 


15 


6 


8 


13 


Pale green 


2 


No. 7. . 


10 


15 


5 


7 


12 


Do. 


2 


No. 8. . 


10 


15 


5 


10 


14 


Do. 





No. 9.. 


13 


17 


8 


10 


16 


Dark green 





No. 10. 


11 


16 


8 


10 


13 


Do. 


1 


No. 11. 


10 


15 


5 


9 


14 


Pale green 


1 


No. 12. 


9 


19 


6 


8 


13 


Do. 






Table 36 shows that in general the plants in containers with nitrates 
added to the first or second foot (viz, Nos. 1, 2, 3, 4, 9, and 10) were taller, had 
a greater number of leaves per plant, and that the leaves were wider and of a 
dark-green color. Thus the nitrates stimulated vegetative growth, but did 
not promote flower production. However, even the best developed plants 



Depths at Which Plants Absorb Water and Nutrients. 103 

had made a very poor growth during the 129-day period (November 4 to 
March 12) when compared with the usual development under field conditions 
(cf. p. 98). Moreover, when the containers were emptied on March 12, so 
that they might be available for use in the field, it was found that the roots 
had made even a poorer development relatively than the tops, since the latter 
were somewhat attenuated because of unfavorable growth conditions. 

While the duration, and especially the intensity, of the light were un- 
doubtedly the chief Hmiting factors to growth (cf. Garner and Allard, 1920), 
brief mention may be made of the other environmental conditions. Thermo- 
graph records show that the air-temperature averaged about 75° F. throughout 
the period. The temperature was maintained within 5° F. of the average 
more than two-thirds of the time. During November the extremes varied 
from 50° to 93° F.; throughout December the range of variation seldom ex- 
ceeded 15° F., a maximum of 90° F. being reached only during two days; 
during January, owing to an unusual amount of clear weather, temperatures 
of 90° to 95° F. were reached on several days, while during February and 
March the extreme range was from 65° to 100° F. Hygrograph records gave 
an average relative humidity for the several weeks varying from 45 to 65 
per cent. During most of the period the average was 50 per cent. Corre- 
lated with the rather uniform temperature, the humidity did not fluctuate 
widely. The minimum fell to 28 per cent on a few occasions, but usually 
varied from 33 to 38 per cent, while the maximum humidity of 85 per 
cent was seldom reached, the usual maxima varying from 60 to 68 per 
cent. The average daily evaporating power of the air recorded by atmom- 
eters placed among the plants was 15.1 c. c. A maximum of 19.5 c. c. was 
determined during the week of December 20 to 27 and a minimum of 12.7 c. c. 
on December 6 to 13. A good water-content was present in the containers 
at all times. 

Thermograph records secured at a depth of 8 inches in the sand, just outside 
the containers, which was kept well watered, gave an average temperature of 
about 70° F. This fell to 65° during one period of two weeks and reached 
75° F. in March. The fluctuation from the mean during any week did not 
exceed 5° F. Records of soil-temperature were also secured at a depth of 
3 feet. Temperature fluctuations here took place very slowly; the total 
variation during the whole period did not exceed 6° F., a temperature of 73° F. 
being rather uniformly maintained. Thus the growth conditions as regards 
soil and air temperature were not greatly unlike those of field conditions in 
June, but quite unlike those under which the field crop makes its early growth. 
Soil and air moisture were favorable, but the short days of relatively poor 
illumination were made still less effective by the glass roof cutting off much of 
the radiant energy. Normally an ordinary clean, double-strength window- 
pane cuts off 40 to 50 per cent of the light (as measured by its effect upon 
solio paper), while dust, moisture, etc., collecting upon the glass reduce this 
amount still further. Aside from this, during midwinter the direct sunlight 
was cut off for about an hour each day, owing to the proximity of other 
buildings. On the other hand, weather records show the period to be one with 
an unusual amount of clear weather. 

On March 12 the containers were opened, the root systems examined, and 
soil samples for water-content and nitrate determinations were taken to com- 



104 Development and Activities of Roots of Crop Plants. 

pare with those at the beginning of the experiment. Great care was exer- 
cised to secure thoroughly representative composite samples for nitrate 
analysis. A small amount of toluene was added at once to the sample in the 
air-tight jars to stop bacterial action. 

Nitrates were determined by the reduction method, using Devarda's alloy 
and the method proposed by Whiting, Schoonover, and Richmond (1920). 
The results of these analyses, together with the data on root extent and water- 
loss, are summarized in table 37. Final analyses for nitrates were made only 
in those fertilized soil layers into which the roots extended. 



Table 37 —Loss of water and nitrates 1 from November 4, 1920, to March 12, 1921. 



Con- 
tainer. 


Depth. 


Water-content. 


Nitrates, p. p. m. 


Root development. 


Nov. 4. 


Mar. 12. 


ra 
O 


! Nov. 4. 


Mar. 12. 


Loss. 




feet. 


p. ct. 


p. ct. 


p. ct. 








A few roots extended 3 or 4 


No. 1 . . 


to 1 


25.8 


12.6 


13 .2 


393.3 


199.4 


193.9 


1 to 2 


25.1 


21.2 


3.9 








inches into third foot. 




2 to 3 


23.6 


21.4 


2.2 










IN . Z . . 


ft +n 1 
U TO I 


24.8 


15.9 


8.9 


390.0 


165.3 


224.7 


A few roots extended 1 or 2 


1 to 2 


26.5 


21.9 


4.6 








inches into third foot. 


No. 3. . 


to 1 


24.5 


15.4 


9.1 








All roots confined to first 2 feet. 




1 to 2 


24.4 


18.9 


5.5 


394.2 


239^4 


154.8 




No. 4. . 


to 1 


26.5 


16.7 


9.8 








Roots evenly distributed, in 




1 to 2 


26.3 


22.7 


3.6 


399.7 


139.6 


260.1 


first 2 feet only. 


No. 5'. 


to 1 


27.1 


20.5 


6.6 








A few roots penetrated 4 to 6 


1 to 2 


29.7 


27.0 


2.7 








inches into second foot. 


No. 6. . 


to 1 


25.1 


18.7 


6.4 








Roots evenly distributed in 


1 to 2 


26.5 


23.8 


2.7 








first 2 feet only. 


No. 7. . 


to 1 


25.8 


17.6 


8.2 








Very few roots below 1.8 feet. 




1 to 2 


26.9 


23.3 


3.6 










No. 8. . 


to 1 


25.9 


19.1 


6.8 








Very few roots below 1.8 feet. 




1 to 2 


27.1 


22.1 


5.0 








Best root development; evenly 


No. 9. . 


to 1 


25.6 


17.4 


8.2 


392.3 


142.4 


249.9 


1 to 2 


25.7 


23.2 


2.5 


397.8 


165.2 


232.6 


distributed in first and second 




2 to 3 


24.6 


22.3 


2.3 


395.7 


39.8 


355.9 


foot and quite abundant to 


















2.5-foot level. 


No. 10. 


to 1 


27.9 


17.9 


10.0 


399.4 


85.4 


314.0 


Evenly distributed in first 2 




1 to 2 


25.5 


24.2 


1.3 


397.3 


54.1 


343.2 


feet only. 


No. 11. 


to 1 


25.8 


16.7 


9.1 


24.2 


21.3 


2.9 


Roots in first 2 feet only. 




1 to 2 


32.1 


21.7 


10.4 


26.6 


11.4 


15.2 


Roots in first 2 feet only. 


No. 12. 


to 1 


24.0 


17.2 


6.8 


19.8 


42.7 


+22.9 




1 to 2 


26.5 


21.7 


4.8 


26.4 


11.3 


15.1 





1 The nitrate-content is given in parts per million of N0 3 . This includes not only the NOs 
of the NaNOa added, but all N0 3 present in the soil when analyzed at the beginning and end 
of the experiment respectively. 

2 This container was taken down on December 21. 



A study of table 37 shows that the roots developed only poorly; in only 
3 of the 12 containers did they reach depths greater than 2 feet. Moreover, 
they were scarcely more than half as abundant as in the earlier field experi- 
ment (p. 94). These findings lead the writers to seriously doubt the value 
of many greenhouse experiments with crop plants when the results are applied 
to field conditions. Not infrequently the indoor environment is made still less 



Depths at Which Plants Absorb Water and Nutrients. 105 



favorable for growth by the use of too little soil in small containers. In every 
case the roots were better branched in the fertilized soil layers, and, correlating 
with the growth of tops, the best root systems were found in containers 1, 2, 
3, 4, 9, and 10. Moreover, in general, greater amounts of water were also used 
by these more vigorous plants, although the water-loss in any case is relatively 
small, even when the 3 or 4 liters added to each container is taken into account. 
The loss of nitrates at all levels is pronounced, the plants in container No. 9, 
which were among the most vigorous of the lot, extracted rather large amounts 
from the third foot of soil, thus indicating that the deeper portion of the root 
system is very active in absorption. 

In order to determine the amount of nitrification or denitrification taking 
place in the soil during the period of the experiment, analyses were made of 
the soils in the control containers (Nos. 11 and 12) at all levels, both at the 
beginning and at the end of the experiment. These data are given in table 38. 



Table 38. — Changes in nitrate-content in unfertilized soil. 





Container No. 11, roots in 
first 2 feet only. 


Container No. 12, roots in 
first 2 feet only. 


Depth. 


Nitrates, parts per million. 


Nitrates, parts per million. 




Nov. 4. 


March 12. 


Loss. 


Nov. 4. 


March 12. 


Loss. 
















feet. 

to 1 . . 

1 to 2 . . 

2 to 3 . . 

3 to 4 . . 


p. ct. 
24.2 
26.6 
65.0 
24.2 


p. ct. 
21.3 
11.4 
25.6 
65.5 


p. ct. 
2.9 
15.2 
29.4 
+41.3 


p. ct. 
19.8 
26.4 
28.6 
28.6 


p. ct. 
42.7 
11.3 
37.0 
42.7 


p. ct. 
+22.9 

15.1 
+ 8.4 
+ 14.1 



Table 38 shows that the soil at all depths was poor in nitrates when taken 
from the field. Leguminous crops had not been grown on the area from which 
the soil was secured for at least three seasons, during which period it had borne 
Sudan grass and oats. In the unfertilized soil layers where roots occurred 
changes in the nitrate-content were small when compared with the large 
amounts removed from the fertilized layers (table 37). In the deeper layers, 
where no roots occurred the increase or decrease in the nitrate-content is 
proportionally small. Thus it may be seen that nitrification and denitrifica- 
tion affect the results given in table 37 to no great degree. 

Field Experiments, 1921. 
Early in the spring of 1921 an extensive series of experiments on the absorp- 
tion of nitrates by several crops was begun. In addition to Manchuria barley, 
Early Ohio potatoes (Solanum tuberosum), and Iowa Silver Mine corn (Zea 
mays indentata), three native grasses were employed. These were wheat-grass 
(Agropyrum glaucum), big bluestem (Andropogonfurcatus), and little bluestem 
(A. scoparius). 

Large oak barrels 1.7 feet in minimum diameter and 2.8 feet deep were 
used in part, especially for the earlier stages of growth, but these were supple- 



106 



Development and Activities of Roots of Crop Plants. 



mented by heavy, water-tight, cylindrical, galvanized-iron containers 2 feet 
in diameter and 3.5 to 4 feet deep, while the one for corn measured 3 feet in 
diameter and 5 feet deep. Sufficient soil to fill the containers was secured from 
both the upland and lowland crop plats north of Lincoln (p. 40) on February 
20 and stored in large piles in a dry place until March 30-31, when it was placed 
in the containers. These soils were chosen because they were from the same 
plats as those used in the preceding experiments and both their mechanical and 
chemical composition had been determined (tables 8 and 9). Care was exer- 
cised to keep the soils from the several levels to 4 feet separated. When 
taken from the field they were in such excellent condition regarding water- 
content that it was unnecessary to add more water when working them over to 
break up lumps, etc. During storage they were kept well covered to reduce 
water-loss. 



May June 

1 2 3 4 1 2 3 4 





























/ 










/ 






/ 






/ 

/ 




t — j 





























































Fig. 41. — Average daily temperature (long broken lines), 
humidity (upper solid line), and average daily 
evaporation at Lincoln, 1921. 



On March 30-31 a large trench was dug in the field where the 1921 crops 
were grown (p. 80), and the containers, 16 in number, placed close together in 
a row in such a manner that the tops were about 4 inches above the surface 
of the soil. The prepared soil from the deeper levels was then poured slowly 
into the containers, where it was tamped into place. When filled, the soil in 
each container (with certain exceptions to be noted) occupied the same relative 
position as regards depth that it had occupied in the field. Barley was grown 
in the lowland soil; potatoes in that from the upland. 

Sodium nitrate was added at certain sealed levels at the same rate as in 
the preceding experiment (viz, 400 p. p. m. of NaN0 3 based on the wet weight 
of the soil). In this series, however, the proper amount for the weighed soil 
at any level was dissolved in about 0.5 liter of water, which was poured upon 
the soil after it had been placed in the container. This facilitated rapid 
diffusion, and it seems probable that within a period of 2 weeks the nitrate was 
rather uniformly distributed throughout the soil-mass. Triplicate samples 



Depths at Which Plants Absorb Water and Nutrients. 107 

for water-content determinations and large composite samples for nitrate 
determinations were secured at all levels at the time the containers were filled 
and before the nutrient was added. 
BARLEY BARLEY POTATOES POTATOES POTATOES 




Fig 42.-Diagram of containers and root development of crops, 1921 Horizontal lines (6 
inches apart, except in last two) indicate position of wax seals and double vertical 
lines position of nutrients. 

When the containers were filled within 2 inches of the tops, two thin wooden 
strips about 1.5 inches in width and as long as the diameters of the containers, 
were placed edgewise and partially sunk into the soil so as to prevent the wax 
seal from covering the area of soil (about 1.5 inches in width) m which the crops 
were to be planted. Finally, the wax seal was covered with 2 inches of sand. 
Next a light-green wooden roof, with sufficient slope to cause the water to 
run off but with an opening 1.5 inches wide and as long as the diameter of the 



108 Development and Activities of Roots of Crop Plants. 



container, was fastened in place. Before putting the wooden strips in posi- 
tion, however, pieces of oilcloth were inserted under them in such a manner 
that one end extended an inch or two under the wax seal, while the other lined 
the inside of the opening between the strips and came up through the roof, 
upon which it was folded back and tacked down. This gave a smooth surface 
against which the plants might later be blown back and forth free from injury 
during windy weather (plate 12 b). In case of the potatoes, a rectangular 
opening about 3 by 4 inches was left in the roof. Similar modifications from 
that described were also made for the corn and wild grasses, the latter being 
planted as sods. A small amount of earth was placed in the opening thus 
left, the crop planted, and a mulch of about an inch of dry sand added to check 
water-loss. Both barley and potatoes were planted on April 1, the halves of 
two potatoes being placed in the soil of each of the several containers at a depth 
of about 4 inches. The barley, as usual, was planted thickly and later thinned 
to the desired stand. 



Table 39. — Loss of water and nitrates April 1 to May 25. 







Water-content. 


Nitrates, parts per million. 




Con- 
tainer. 


Depth. 


u 

a 
< 


>> 

a 


m 

QQ 

o 

h3 


rH 

a 

< 


Gain by 
nitrifi- 
cation. 1 


<N 

tt 
3 


03 

cn 
O 


Root development. 




feet. 
to 0.5 


p. ct. 
28.5 


p. ct. 
19.7 


p. ct. 

8.8 










Roots very abun- 
dant to 1.5 ft.; also 




0.5 to 1 


28.6 


22.5 


6.1 










No. 1. 


1 to 1.5 
1.5 to 2 


25.0 
25.0 


22.3 
24.8 


2.7 
0.2 


376.4 


137.5 


346.0 


167.9 


extended through- 
out the 1.5 to 2 foot 




2 to 2.5 


23.8 


24.7 


+0.9 










layer, but were rel- 
atively few. 
Roots very abun- 
dant to 2 ft., be- 
yond which the en- 
tirely unbranched 
tips extended for 
only 2 or 3 inches. 




to 0.5 


29.9 


22.3 


7.6 












0.5 to 1 


28.3 


20.8 


7.5 










No. 2 . • 


1 to 1.5 


25.2 


19.9 


5.3 












1.5 to 2 
2 to 2.5 


24.2 
24.7 


23.0 
24.5 


1.2 
0.2 


373.2 


137.5 


365.7 


145.0 



















» The gain by nitrification has been calculated here, as in the following tables, from data 
obtained from the control container (see table 41, p. Ill), on the assumption that the increase 
by nitrification varied directly with the time. 



After the soil had been replaced about the containers in the trench and 
ridged up in such a manner as to insure drainage away from them, barley 
was planted thickly on both sides of the row of containers and in this manner 
field conditions were approximated (plate 12). During the hotter part of 
the season the wooden roofs were covered with a mulch of straw to lessen the 
intensity of the heat. Brome-grass was sowed about the containers in which 
wild grasses were growing, while the corn was placed in the middle of a small 
corn-field. 

As pointed out on page 88, weather conditions were very favorable for 
rapid development of the crops, the ripening of the small cereals occurring 
at least two weeks earlier than normally in eastern Nebraska. The average 
daily temperature, humidity, and evaporation are shown in figure 41. 



Depths at Which Plants Absorb Water and Nutrients. 109 



On May 25, when the barley had reached an average height of 1.6 feet 
(maximum height 1.7 feet) and was unfolding the sixth or seventh leaf, con- 
tainers Nos. 1 and 2 were examined (plate 12 b). The soil in these containers 
was fertilized at the 1 to 1.5 and 1.5 to 2 feet depths respectively, wax seals 
being inserted both above and below these levels. The position of these 
layers, together with the root development, is shown diagramatically in figure 
42. It may be noticed that the roots in container 1 are not so abundant below 
the 1.5-foot level as in container 2. The presence of the fertilized layer in the 
first container evidently caused this phenomenon, which, in fact, was observed 
in several other cases. Wherever the roots of any of the crops entered fer- 
tilized soil, the degree of branching was very much more pronounced. Table 
39 gives a summary of the water and nitrate losses during this 55-day period. 

A study of table 39 shows that the roots absorbed almost as much water 
from the second 6-inch layer of soil as from the first, and also that the water- 
content below the seal in the 1 to 1.5 foot layer was considerably reduced. 
The nitrate-content of the soil, as in the following tables, includes not only 
the NO3 of the NaNCh added, but all NO3 present in the soil when analyzed 
at the beginning and end of the experiment, respectively. The nitrate- 
losses at depths of 1 to 1.5 and 1.5 to 2 feet respectively show clearly the root 
activities at these levels. 

On June 13 the barley in containers 6, 7, and 8, and the potatoes in con- 
tainers 3, 4, and 5 were examined. The barley had developed quite evenly 
with that grown outside of the containers and was in the blossoming stage, 
although a few of the older heads had begun to fill. The plants had tillered 
well. The crop had an average height of about 2.8 feet, except that those 
plants in container 7, which had been slightly damaged by frost, were only 
about 2.5 feet tall (maximum 3.2 feet, plate 13 a). The potatoes were 1.7 
to 2 feet tall, had developed normally as compared with those in an adjoining 
field, and were just beginning to blossom. The position of the wax seals 
inclosing the fertilized soil layers and the extent of the root development is 
shown in figure 42. Here again the effect of the fertilized soil upon limiting 
root penetration, as well as increasing the degree of branching, is patent. 
That the wax seal offered no obstacle to root penetration is clearly shown in 
plate 9 c, where a portion of the seal taken at a depth of 2 feet from container 
8 is shown. The high degree of root development in this fertilized layer (depth 
2 to 2.5 feet) is also shown in the same plate. Glass funnels 3 inches in 
diameter and partly filled with coarse sand were placed inverted in the several 
containers at depths indicated in table 40. These were connected with large 
glass tubes which extended 2 inches above the soil-surface, where they were 
kept corked. These furnished a means of adding water to the soil. The 
loss of water and nitrates, together with the crop development, is given in 
table 40. 

A survey of table 40 shows that the amount of water absorbed by the 
potatoes, while not so great as in the case of barley, was quite uniform in 
the several containers and corresponds well with root depth and distribution. 
The nitrates removed at the different levels, while quite marked in amount, 
were also less than that used by barley. Water-losses from the containers 
with barley were greatest from the first foot (7 to 13 per cent), but large 
quantities had also been removed from the second-foot layers (2 to 7 per cent), 



110 Development and Activities of Roots of Crop Plants. 

Table 40. — Loss of water and nitrates, April 1 to June IS. 



Container and crop 
development. 



No. 3. Potatoes, 3 stalks, be- 
ginning to blossom; 10 tu- 
bers 3 to 10 mm. in diam- 
eter; roots unevenly distrib- 
uted to a depth of 1.5 ft., 
none deeper, as abundant 
in fertilized layer as else- 
where and more profusely 
branched. 

No. 4. Potatoes, 3 stalks, 
more leaves than in No. 3; 
eight tubers 1 to 30 mm. in 
diameter; roots fairly abun- 
dant to 1.5 ft., less abun- 
dant to 2 ft., below which 
none penetrated. 

No. 5. Potatoes, 2 stalks, be- 
ginning to blossom; 8 tubers 
2 to 20 mm. in diameter; 
roots fairly abundant to 1.5 
ft., some reaching a depth 
of 2 ft. 

No. 6. Barley, 67 stalks 
with heads, many small 
stalks without heads; roots 
abundant to 1.5 ft., fairly 
abundant to 2 ft., below 
which they were sparse. 

No. 7. Barley, 60 stalks 
with heads, smaller stalks 
without heads, not so well 
developed as in 6 and 8; 
roots very abundant to 2 ft., 
below which none was found. 

No. 8. Barley, 75 stalks 
with heads, similar to No. 
6; roots abundant and even- 
ly distributed to 2.5 ft., only 
more branched in 2 to 2.5 
ft. layer. 



Depth. 



feet. 

to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 



to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 



to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 

to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 

to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 

to 0.5 
0.5 to 1 

1 to 1.5 
1.5 to 2 

2 to 2.5 



Water-content. 



p. ct. 
22.1 
21.9 
22.5 
22.8 
25.3 



25.9 
25.3 
22.0 
21.8 
23.8 



25.2 
25.4 
23.7 
24.8 
23.5 

29.0 
25.6 
24.7 
24.4 
23.6 

27.8 
26.7 
24.6 
23.2 
21.8 

28.4 
23.8 
24.0 
24.8 
22.4 



p. ct. 
18.0 
18.5 
21.3 
22.8 
24.6 



20.8 
20.9 
20.2 
20.6 
22.9 



21.0 
21.6 
20.5 
24.2 
23.7 

15.7 
13.5 
19.0 
20.4 
22.6 

21.3 
19.1 
19.6 
20.9 
22.6 

14.4 
15.1 
16.6 
18.2 
20.7 



p. ct. 
4.1 
3.4 
1.2 
0.0 
0.7 



5.1 
»4.4 
1.8 
1.2 
0.9 



»4.2 
3.8 

i3.2 
0.6 
+0.2 

13.3 

212.1 

5.7 
4.0 
1.0 

6.5 
"7.6 
5.0 
2.3 
+0.8 

14.0 
»8.7 

7.4 
»6.6 

1.7 



Nitrate, parts per million. 



363.5 



361.7 



375.4 



371.0 



era 



185.0 



155.4 



405.0 



447.0 



185.0 



155.4 



408.7 



103.6 



274.0 



391.0 



143.5 



70.1 



286.4 



135. 



344.0 



168.3 



i Two liters of water were added to the soil at this depth during the growth of the plants. 
» Seven liters of water added. 
• Four liters of water added. 

while in some of the containers, especially No. 8, where the fertilized layer 
was deep, the roots had penetrated well below 2 feet and had carried on 
considerable absorption. Barley roots were active not only in absorbing 
water, but they were also removing the nutrient in considerable amounts. 
The loss at 2 to 2.5 feet depth (168.3 parts per million) is especially striking. 

The barley was ripe on July 1, the heads being well filled. However, it 
was allowed to stand until July 9, when it was finally examined, along with 



Depths at Which Plants Absorb Water and Nutrients. Ill 

the potatoes, the tops of which were ripening rapidly. At this time the 
soil in container 9, which bore no crop, was also examined. The results 
obtained from this examination are given in table 41. 



Table 41. — Loss of water and nitrates, April 1 to July 9. 



vUU wcUUd ctllvJ. tiup 
H av a i n ~n TYi p n t 


Depth. 


Water-content. 


Nitrates, parts per million. 


Apr. 1. 


July 9. 


Loss. 


Apr. 1. 


Gain by 
nitrifi- 
cation. 


July 9. 


Loss. 




feet. 


p. ct. 


p. ct. 


p. ct. 










No. 9. Control. No plants. 


to 0.5 


24.7 


22.9 


1.8 


0.0 


210.0 


210.0 


+210.0 


0.5 to 1 


24.5 


23.8 


0.7 


0.0 


251.0 


251.0 


+251.0 




1 to 1.5 


25.0 


24.8 


0.2 


11.4 


252.6 


264.0 


+252.6 




1.5 to 2 


22.9 


22.5 


0.4 


11 .4 


204.6 


216.0 


+204 . 6 




2 to 2.5 


24.1 


23.2 


0.9 


51.3 


140.7 


192.0 


+ 140.7 


No. 10. Potatoes, 3 stalks 


to 0.5 


28.5 


23.8 


4.7 










1 5 to 2 ft tall* 4 tubers 


0.5 to 1 


24.3 


22.3 


i2.0 










1 to 2 in. in diameter, sev- 


1 to 1.5 


24.4 


20.3 


4.1 










eral rtti ft Hpr nnps T?.ootfl 


1.5 to 2 


23.1 


20.8 


2.3 


364.4 


204.6 


341.0 


228.0 


abundant to 2 ft., fairly- 


2 to 2.5 


23.1 


21.0 


2.1 


358.7 


140.7 


423.0 


76.4 


abundant to 2.5 ft. 


















No. 11. Potatoes, 2 stalks 


to 0.5 


27.8 


19.7 


8.1 










2 ft. tall, 2, 1.7 ft. ; 6 tubers 


0.5 to 1 


23.4 


21.5 


»r.9 










about 1.5 in. in diameter, 


1 to 1.5 


24.6 


21.3 


3.3 










several smaller ones * roots 


1.5 to 2 


23.3 


20.4 


2.9 










flbiinHnnf'. t,n 1 R ft, nnlv 


2 to 2.5 


22.7 


21.7 


1.0 


358.3 


140.7 


334.0 


165.0 


a few penetrated deeper. 


2.5 to 3 


24.5 


23.9 


0.6 












3 to 3.5 


19.3 


20.4 


+1.1 










No. 12. Barley, 154 stalks 


to 0.5 


24.8 


23.5 


«1.3 










with 101 large well-filled 


0.5 to 1 


24.6 


14.8 


9.8 










heads, ave. ht. 2.5 ft.; 


1 to 1.6 


25.9 


19.8 


*6.1 










roots abundant to 2.5 ft., 


1.5 to 2 


24.8 


17.4 


7.4 










beyond which few pene- 


2 to 2.5 


27.4 


21.1 


6.3 


412.2 


140.7 


413.0 


139.9 


trated. 


2.5 to 3 


23.6 


24.1 


+0.5 












3 to 3.5 


22.7 


21.8 


0.9 










No. 13. Barley, 135 stalks 


to 0.5 


27.3 


19.0 


8.3 










with 112 large, well-filled 


0.5 to 1 


26.3 


14.3 


»12.0 










heads, av. ht. 2.5 ft. ; roots 


1 to 1.5 


24.2 


17.2 


7.0 










abundant to 2.5 ft., fairly 


1.5 to 2 


25.2 


17.9 


«7.3 










abundant to 3 ft., beyond 


2 to 2.5 


25.4 


22.8 


2.6 










which a few penetrated 3 


2.5 to 3 


24.7 


23.0 


1.7 


415.3 


140.7 


370.0 


186.0 


to 5 inches. 


3 to 3.5 


24.1 


24.9 


+0.8 












3 to 3.5 


23.0 


23.6 


+0.6 











1 Eight liters of water were added to the soil at this depth during the growth of the plants. 
« Five liters of water added. 
3 Six liters of water added. 



In table 41, the control container shows marked gains by nitrification at 
all depths. The water-losses from this container, except for evaporation 
through the slit in the roof from the surface 6 inches, fall well within the 
experimental error of sampling. The potatoes had reduced the water- 
content to the depth of root penetration, while the absorption of nitrates 
was also in close agreement with root distribution. So few roots penetrated 
beyond 2.5 feet that nitrate-losses at this depth were not determined. 



112 Development and Activities of Roots of Crop Plants. 

The water used by the barley in container 12 was very similar in amount 
at all depths to which the roots were abundant (2.5 feet) ; that in container 
13 was less below 2 feet. A comparison of these losses with those from 
plants unearthed on June 13 (table 40) shows clearly the great activity of 
the deeper and younger roots during the interval between blossoming and 
maturity. The loss of nitrates at 2 to 2.5 feet was less from container 12 
than from container 8, which was excavated on June 13. However, the 
absorption at 2.5 to 3 feet (186 parts per million) shows conclusively the 
activity of the younger roots. 

Iowa Silver Mine corn was planted on May 4. The cylindrical container, 
which was 3 feet wide and 5 feet deep, was sunk into the soil in the center 
of an area which was planted to corn (plate 14 a). The fourth and fifth 
foot were filled with soil from the 4-foot level from the lower crop plats. 
This had been impregnated with the usual amount of sodium nitrate, wax 
seals being placed at depths of 3 and 4 feet. The third foot was filled with 
impregnated soil from the corresponding level from the lower crop plats 
and separated by a wax seal from the first and second foot of surface soil, 
taken from the crop plats where the experiment was conducted. Only a part 
of the surface was covered by the seal, a circular area about 10 inches in diam- 
eter in the center of the container being covered by sand only. Two 5-inch 
funnels, inverted and partially filled with sand and connected with large 
glass tubes which passed through the wooden roof, afforded means of watering 
the first and second foot of soil. Three stalks of corn were grown in the hill 
in the center of the container. The crop developed rapidly, reaching a maxi- 
mum height of 11.3 feet when the pollen was shedding on July 10 (plate 14 b). 

Growth conditions (discussed on p. 88; cf. also fig. 41) remained favorable 
during July and the first half of August. Warm weather with abundant 
rains caused the crop to thrive, the corn in the container being furnished the 
necessary water, from time to time, through the funnels. In this manner 
50 liters of water were added to both the first and second foot of soil, while 
on July 25 the roof and surface seal were removed and 20 liters of water were 
poured slowly on the soil. This was repeated on August 2, when 12 liters 
were added. After each watering a mulch of straw covered with sand was 
put on the surface before the wooden roof was replaced. 

The container was excavated and the contents examined on August 15. 
At this time the three large stalks were 10.5 to 11.5 feet tall, about 1.2 inches 
in diameter at a height of 2 feet, and each had a large ear about 10 inches long 
at a height of 6 feet. The lower leaves were drying and the kernels were 
well filled and beginning to dent. 

The first 2 feet of soil (from which no samples were taken) were very well 
occupied by roots and were quite dry, the first foot breaking up into lumps. 
The roots had penetrated the seal at 2 feet and branched so abundantly in the 
fertilized soil below that they were even more abundant than in the surface 
soil. Every cubic centimeter of soil seemed well filled with roots. In the 
fourth foot the roots were very abundant, but somewhat fewer than in the 
third-foot layer. Below 4 feet the roots were sparse; none extended deeper 
than 4.5 feet. The cause for the shorter root system (the corn roots outside 
reached depths of over 5 feet) was undoubtedly due to the rich subsoil. 
The long, white, unbranched root-ends indicated that growth was not yet 



Depths at Which Plants Absorb Water and Nutrients. 113 



complete. The losses of water and nitrates in the sealed layers are given in 
table 42. 

Table 42. — Loss of water and nitrates, May 4 to August 15. 





Water-content. 


Nitrates, parts per million. 


Depth. 


May 4. 


Aug. 16. 


Loss. 


May 4. 


Gain by 
nitrification. 


Aug. 15. 


Loss. 


feet. 
2 to 3 


p. ct. 
22.1 


p. ct. 
17.8 


p. ct. 
4.3 


407.8 


144.2 


349.0 


203.0 


3 to 4 


21.9 


18.4 


3.5 


395.4 


133.9 


389.0 


140.3 


4 to 5 


25.8 


23.2 


2.6 


407.1 


133.9 


423.0 


118.0 

















Absorption of water at the various depths is directly correlated with the 
abundance of roots and the time the roots were present and active at the 
several levels. The nitrate losses, while decreasing with depth as one would 
anticipate, are sufficiently marked to show clearly that in studies of soil 
fertility more than the surface soil must be taken into account. 

The native grasses were planted as blocks of sod approximately 8 inches 
long, 5 inches wide, and 6 inches deep. These were secured from the field on 
May 4, when the new growth, which was cut back, was about 3 inches high. 
The containers in which they were placed were filled with lowland soil to 
which nitrates had been added at depths of 1 to 2.5 feet, seals being inserted 
in the fertilized soil at depths of 1 and 2 feet respectively. The surface foot 
of soil consisted of the rich loam taken from the crop plats. No seal or sand 
was used on the surface. Openings the size and shape of the surface of the 
sods were cut in the roofs to permit the growth of the grasses from the entire 
blocks. The first foot of soil was kept well watered and the grasses grew very 
rapidly. By July 20 flowering stalks had begun to appear, and by August 15, 
when they were examined finally, they had made an excellent growth. Agro- 
pyrum glaucum was 2.5 feet tall, but had not headed out, while Andropogon 
{meatus had flowering stalks 4 to 6.7 feet tall, some of which were beginning 
to blossom (plate 13 b). Unfortunately, Andropogon scoparius, which had 
also made an excellent early growth, became waterlogged and could not be used. 



Table 43. — Loss of water and nitrates, May 4 to August 15. 







Water-content. 


Nitrates, parts per million. 


Plant. 


Depth. 




HI 
< 


m 
o 


>> 


Gain by 
nitrifi- 
cation. 


si 
< 


m 

QQ 

o 


Agropyrum glaucum 


feet. 

1 to 2 

2 to 2.5 


p. ct. 
24.0 
24.7 


p. ct. 
18.2 
21.3 


p. ct. 
5.8 
3.4 


371.9 
415.3 


236.9 
144.2 


485.0 
337.0 


123.8 
222.5 


Andropogon furcatus 


1 to 2 

2 to 2.5 


23.7 
28.7 


15.0 
25.9 


8.7 
2.8 


372.3 
427.1 


236.9 
144.2 


231.0 
246.0 


378.2 
325.3 



114 Development and Activities of Roots of Crop Plants. 

Wheat-grass roots were very abundant to the bottom of the container 
(depth 2.5 feet) where they were slightly massed. They penetrated thor- 
oughly all portions of the soil, but were especially well branched in the fer- 
tilized layers below the first foot. The roots of the big bluestem were also 
splendidly developed and especially abundant in the second foot. They 
had not filled the third foot of soil so completely as the wheat-grass. Water 
and nitrate absorption by the grasses is given in table 43. 

The amount of water used by the grasses is rather remarkable when the 
brief period of growth is taken into consideration. However, studies of the 
life-history of grasses (Clements and Weaver, 1921) impress one with the 
rapidity of root development. The removal of nitrates is also very marked, 
exceeding considerably in amount that removed by any crop plants used in 
these experiments. 

SUMMAKY. 

The great depth to which the roots of both native and crop plants penetrate 
has led the writers to perform a series of experiments to determine the 
amount of water and nutrients absorbed from the deeper soils. In these 
experiments containers 1.5 to 3 feet in diameter and 2.5 to 5 feet deep were 
employed. They were placed in trenches, which were then refilled with soil 
and crops planted around the containers in such a manner that the experi- 
mental crops in the containers were grown under field conditions. The con- 
tainers were filled with well-mixed soil of known water-content and physical 
and chemical composition, to which, at certain levels, NaN0 3 had been added 
at the rate of 400 parts per million. The containers were filled in such a 
manner that the well-compacted soil at any level occupied the same relative 
position as regards depth that it had occupied before removal from the field. 
The fertilized layers, and in some cases every 6-inch layer, were separated 
from the rest of the soil by wax seals which prevented the movement of water 
or solutes, but through which the roots readily penetrated. To prevent water 
intake each container was furnished with an appropriate wooden roof. The 
experiments extended over a period of 2 years, during which time the following 
crops were grown: oats, barley, potatoes, corn, and two native grasses (Agro- 
pyrum glaucum and Andropogon furcatus). In order to study the activities 
of the roots at various stages in their development, enough containers were 
used (about 50 in all) so that some could be examined at each of the several 
periods of growth of the crops. 

Preliminary experiments with oats showed that this crop absorbed water at 
all depths to 2.5 feet, even before blossoming. The amount of water absorbed 
by barley from the deeper soils (to 3.5 feet) is in direct relation to the growth 
of the root system into these deeper layers. The total amounts absorbed to 
depths of 2.5 feet were in general practically the same from the several 6-inch 
levels. Corn is an extravagant user of water, absorbing large quantities from 
the third and fourth foot of soil and smaller amounts from the fifth foot. 
Potatoes absorbed water to depths of 2.5 feet (approximately the limit of 
root extent), while the native grasses, grown from transplanted sods, showed 
marked absorption to a similar depth. 

Barley at the age of 54 days had removed 168 and 145 parts per million of 
nitrates from the 1 to 1.5 and 1.5 to 2 foot soil-levels respectively. When in 



Depths at Which Plants Absorb Water and Nutrients. 115 



blossom (19 days later) it had removed 286 and 135 parts per million of the 
nitrates from similar levels, and 168 parts per million from the 2 to 2.5 foot 
level. At maturity it had removed 186 parts per million from the 2.5 to 3 
foot level. Potatoes used the nitrates in smaller amounts. When beginning 
to blossom (74 days old) they had removed 143 and 70 parts per million of 
nitrates from the 1 to 1.5 and 1.5 to 2 foot layers respectively, and when 
beginning to ripen (100 days old) 228 parts per million had been removed 
at a depth of 1.5 to 2 feet, and 76 to 165 parts per million at the 2 to 2.5 foot 
level. Agropyrum and Andropogon used nitrates from the second and third 
foot in large amounts (124 to 378 part per million), while corn removed 203, 
140, and 118 parts per million at depths of 3, 4, and 5 feet respectively. 

Under greenhouse conditions both tops and roots of barley developed so 
poorly that little value is attached to such experiments when applied to field 
conditions. However, the absorption of water and nitrates to 2.5 feet (the 
maximum depth of root extent) correlated nicely with root position and 
development. 

In every case where roots came in contact with a fertilized layer they not 
only developed much more abundantly and branched more profusely, but such 
a layer apparently retarded normal penetration into the soil below. Thus it 
seems that the depth at which the fertilizer is placed in field practice would 
considerably affect root position and development. Fertilizing the surface 
layers of soil in regions where these have very little or no available water 
during periods of drought would appear to be distinctly detrimental to normal 
crop production. Finally, since the roots of crop plants are found to penetrate 
just as deep, or even deeper, under field conditions as in the containers used 
in these experiments, and since their development in every respect has been 
found to be identical, we must conclude that the deeper soils are not only suited 
to plant-life, but that they play an exceedingly important part in the life of 
the plant and deserve careful consideration in a study of crop production. 



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116 



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117 



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PLATE 1 




A. Iowa Silver Mine corn 57 days old; root system shown m figur< 
B Potato 2.3 feet high on July 8; root system shown m figure 11. 

C. Corn on September 2; root system shown m figure 9. 

D. Trench used in examining the roots of cereals. 



PLATE 2 




PLATE 3 



4 




A. White Kherson oats from a square meter at Burlington (left), PhilKpsburg, and Lincoln. 

B. Manchuria barley from a square meter at Burlington (left), Phillipsburg, and Lincoln. 



PLATE 4 



■r- 



A Four hundred plants of alfalfa from lower crop plats(left) and upper crop plats at Lin- 
coln; and from Phillipsburg and Burlington, respectively. 

B Three hundred plants of sweet clover from lower crop plats (left) and upper crop plat, 
at Lincoln; and from Phillipsburg and Burlington, respectively. 



PLATE 5 




A. Wheat from Lincoln (left), Phillipsburg, and Burlington, May 18-21. 

B. Barley from Lincoln (left), Phillipsburg, and Burlington, May 18-21. 



/ 



( 



A. Oats at Lincoln, May 18. 

B. Oats at Phillipsburg, May 19. 

C. Oats at Burlington, May 20. 



PLATE 7 




i 




A. Oats at Lincoln, June 10. 

B. Oats at Phillipsburg, June 10. 

C. Oats at Burlington, June 10. 



PLATE 9 





A. Barley grown in container with wax seals at 6-inch intervals. 

B. Same with upper portion of container removed. 

C. Wax seal at depth of 2 feet (left) showing the penetration of the seal by roots and 

their abundance under field conditions. Fertilized soil at 2.5 feet depth rilled 
with copiously branched roots. 
T>. Arrangement of containers in greenhouse experiment, 1920-21. 



PLATE 10 




A. Development of barley on December 11 in unaerated, fertilized soil. 

B. Development of barley on December 11 in aerated, unfertilized soil. 



PLATE 11 




A. Development of crop on March 12 in fertilized soil. 

B. In unfertilized soil. 



PLATE 12 




A. General view of one row of containers, May 17. 

B. Detailed view of barley and potatoes, May 17. 



A, Potatoes and barley on June 13. 

B. Native grasses on August 15, at the time of examination. 



A. Development of corn, June 5. 

B. Development of corn, July 10. 



S '22 



